Yes, a modern tablet device could never compare to an equally modern desktop PC in terms of power and capacity. They're in entirely different leagues. The sorts of games able to run on the latter could never run on the former, i.e. you won't be seeing a game like Beyond: Two Souls or Destiny on a tablet for many years to come, not without some serious stripping of features, content, and graphics performance.
Take WoW again as an example; I need a keyboard for my many (many) keybinds, a mouse for movement (because keyboard turners are just bad), and, really; an 8" monitor? Please. Tablets are simply a non-starter for complex (in terms of input and required reaction speed) games.
Tablet gaming is for my Mom and myself when I'm bored waiting at an airport. Sure, it's a huge market, but not all gamers are satisfied with Candy Crush.
As an aside, I would love for you to enlighten me as to how my first post could be improved.
I also have to disagree with your dismissal of horsepower as the root of the issue, because I can currently hook up any keyboard, mouse, or even game controller I want to my phone or tablet. Additionally, some portable devices are capable of hooking up to a larger screen via a microHDMI port. Their only limitation, then, would be the internal hardware components that ultimately add up to their "horsepower", with the added advantage of portability.
Also, if I have a tablet with as much horsepower as my desktop then it would necessarily be more expensive than said desktop. So, you're proposing that I buy a tablet which is more expensive than my desktop and hook it up to all the peripherals I need so that I can... wait, what is the advantage here exactly?
You say that I gain portability; right, as long as I bring along my keyboard, mouse, and a monitor. Now that's what I call portability! Certain games just don't work without a large screen and more advanced input devices. Again, completely different markets.
As an aside, since you obviously took exception to my terminology, note that I put quotes around "casual" and "real" for a reason. I don't mean to look down upon the casuals, but to believe that they are basically one in the same is just ignorant. Those in either segment have very different tastes and want very different things from the games they play. I want games with depth that I can sink endless hours into. My girlfriend wants an occasional distraction. You're never going to sell us on the same marketing lines. We want different things.
Surprising to very few, this distinction just so happens to align pretty damn close with the alleged "casual"/"real" divide.
(Also, you've been able to dock laptops for years, that isn't some sort of neat "Surface-like-device" trick, yet all the "real" gamers that I know still own dedicated desktop machines. Their screens, keyboards, mice, and controllers are all bulky. Their setup is already the antithesis of portable, going through all that trouble just to use a docked underpowered device just doesn't make sense.)
Yes, the touch interface sucks for hardcore gaming. But it's not implausible that somebody would figure out the least-obtrusive way to add good gamer-friendly controls to a tablet and a big vendor throws their weight behind this. Then what happens? Then suddenly the big difference between a tablet and a PC gamer is hardware, and tablet gaming suddenly eats up the indie market and starts moving north.
Sure, a PC can push a lot more polies, and so will always have a certain market of core gamers... but look at how Blizzard has always done well targeting aging hardware. The lion's share of the market doesn't have a bleeding-edge video card.