That's partly true but you're ignoring a few things, in my estimation. What's the difference between a tablet with a separate keyboard and mouse peripheral, and a laptop? Ummm... I will grant that it's marginally more portable, but otherwise, is there a functional change? But ok, let's say that portability alone makes it more likable than a laptop. How about the factor of price? Now, perhaps the trend will reverse in the near future, but I can guarantee you that as it stands, size of the machine almost always correlates positively with its power. I have a desktop and a laptop and I've used a tablet, all of which were purchased within a year of one another (actually, the desktop is a wee bit older admittedly) and the power of each is pretty much fits this correlation. The new iPads have some pretty nice capacity for graphics... for a mobile device. They have pretty good memory... for something using flash memory. They have a good processor... can you guess compared to what? Now, they could hypothetically make a tablet as powerful as my desktop, but it would be thousands of dollars. The best iPads right now cost half as much as my far better desktop did nearly 2 years ago, and I'm willing to bet they aren't half as powerful, with a small fraction of my RAM and disk space. Will tablets get better? Yeah, definitely. Will good tablets cost less? Yep. Will better still desktops keep getting released and will they be cheaper than comparable tablets? I'd put money on it. You can already see the model in laptops vs desktops. A laptop that can compete with my desktop in terms of power is much more expensive than the desktop, and not as modular. You can't upgrade a tablet. You cant give it more RAM to keep up with new trends and needs, you can't replace the graphics card, you can't even replace the disk. This alone degrades the value of the device significantly as a gaming platform. You say that gamers don't need the open space of current desktop and laptop OSs? Some, probably. Have you ever wanted to install a mod in Skyrim? Thousands and thousands of gamers don't just want to be able to do that, they do, and they expect every game to be able to handle that. On a closed OS you see on tablets, you can't do that stuff without significantly hacking the device. The tablet's closed system is not, currently, as viable as you are arguing for PC gaming for that reason alone. It's not that I disdain tablets, or think it's bad that people will start using them more (they will, heck I've been thinking of getting one soon), but I don't think, in their current state, they will be competition for the value of the desktop or laptop computer for things like work and gaming, until there's some serious changes to them. I think they will become an ubiquitous part of using the internet and entertainment (and yes, this does include games - of a certain variety) but for work (especially programming, but that's my professional bias) and "hardcore" (for lack of a better term on my tongue right now) gaming, the current desktop/laptop system is hard to beat on functionality, power, price point, and modifiability. For a user friendly experience, tablets will get better, and they'll get better at those other things as well. But I'm not as willing to jump to the assumption that they will be best any time soon.
I still think you're looking at this from the perspective of someone who values a relatively open OS. Many of the design decisions Apple made in producing the original iPad were made in order to mitigate some of those concerns. It doesn't matter that an iPad processor can't stand up next to a desktop processor, because iPad's don't multitask. It doesn't matter that they have relatively little memory compared to a desktop, because it's made for apps that use memory less aggressively. It doesn't matter that a desktop or laptop will beat a comparably priced tablet in nearly every spec because 95% of the people using them don't care about specs. They have a dozen or so things they want their tablet to do well, and it does those things reasonably well. But more importantly, it makes doing those tasks easier and less frustrating. That's a shift of paradigm. For a very long time, manufacturers have been building machines with the notion of stretching what's possible with a computer. But we're at the point where even the most basic computers on the market can do nearly everything that your average home user would want them to do. The new goal is to focus new machines on providing the best possible experience, and you don't do that by generalizing. Mobile operating systems are all about focusing on a single task or two, and making those tasks as easy and simple to carry out as possible. The "gamers want power and options" rationale may seem overwhelming to a dedicated gamer, but the fact of the matter is that desktops and laptop sales declined 4.6% last year. Smartphones outsold them for the first time last year, and tablet sales are rapidly catching up. Pew routinely reports that people are using mobile devices to get on the Web—to the exclusion of laptops and desktops. Your rationale also ignores the changing demographics within the gaming community itself. Social and mobile games are the most rapidly growing segment of the market. Changes in accessibility mean that indie game makers are increasingly developing for mobile and console/downloadable. Desktops are still the domain of the AAA developer, but they're increasingly catering to a demographic that's willing to pay top-dollar for a very specific experience. As I said before, I don't think desktops and laptops are in danger of extinction any time soon—just that they're going to become the domain of specialists. I do most of my computing on a laptop, but I recognize that I'm part of a shrinking minority in that regard. Very few people are programmers or writers with their own website. Most of us simply don't need computers the way they've traditionally been.