If you spend much time on Twitter, you will eventually run into someone who is convinced that the reign of consoles is numbered, that they are about to finally lose to something far, far superior: the iOS platform. A lot of the time, these people are obvious morons, but sometimes you'll hear otherwise smart people saying the same things (and very clearly believing it), not because they're trying to troll you, but--usually--because they don't understand the appeal of consoles and very probably haven't for years.
I usually just listen to those comments and brush them off, but I'm feeling grumpy today because we just saw an amazing E3 that showed us what consoles have in the works... and still, those same people are barely impressed at all by consoles (if that) and ready to declare iOS the victor or a "game changer" even before the game has really begun. So here it is, the one reason iOS will almost certainly never pose a serious threat to consoles: screen size.
You can tell me all you like about how iOS has a controller coming--so that you don't have to deal with the horrendous touchscreen controls anymore--and you can talk about comparative price--only $1 to $3 for a total turd of a shovelware title that you'll argue doesn't have to be all that good anyway because it doesn't cost a lot of money--and you can even regale me with tales of all the phenomenal features that iOS has that consoles never will (which I guess works out to a calendar and, uh... well, there's probably other stuff too that I should be excited about). What you can't get around is the fact that--due to very obvious portability requirements--the screen size on an iOS device is really quite small.
There's nothing wrong with that small screen, per se. It works great on small devices, but screen size changes how a person plays games. I discovered this myself when I recently picked up a 60" television. Even familiar games suddenly played much differently. The timing was all wrong, the sense of scale was much more impressive, and my ability to watch the whole screen in a multiplayer match went bye bye. A larger screen makes for a different experience, and sometimes to a dramatic degree. That's particularly true if a game was made by capable developers who are developing specifically for certain dimensions.
Even if iOS devices are soon fitted with proper controllers as a matter of course--an unlikely scenario, but let's run with it--and provided the means to output to your television, they're not going to produce images that look anywhere close to what blockbuster console games will provide. It takes a lot more power to make something beautiful that fills the whole screen than it does to paint a gorgeous picture on a 10-inch canvas.
As long as consoles stay far enough ahead of the technical curve that can conveniently be included as part of an affordable iOS device (not something that's especially difficult to do with a dedicated console, though the console manufacturers have been slacking off in that department as of late or we wouldn't be having this conversation in the first place), consoles will always have the advantage. The console industry will need to make a series of ridiculous mistakes in order to fall in the face of any iOS onslaught. If anything, the console has more to fear from a completely different multi-purpose device: the PC.
iOS? People who develop apps for that platform can keep churning out 50 new free-to-play and shovelware titles every day, flooding the marketplace with so many too-similar disasters that eventually, even the bravest iOS consumers will decide that finding games that are actually worth playing on that platform simply isn't worth the hassle. If anything, I see the iOS platform's days as a popular gaming device as being numbered...