Console cycles are too long.
The technology in them becomes stagnant too quickly.
Games advance at a faster rate and have to hold themselves back, in a sense.
PC gaming, however, evolves alongside the games, some times faster then they do.
Given that when the current generation of consoles came out they were priced at around $800 for a PS3, you will now have, for the first time, price parity between the two. You can pick up a good PC for that much money these days that will leave you with a solid platform to improve upon. A console cannot do that.
Sure, a console will be able to play everything in its cycle, but there are many holes in that logic, just look at Skyrim on the PS3. The console should be able to handle the game, that is what consumers have paid for, and yet it just can't.
In my mind, what we see as console gaming is under threat. The XBoxs, Wiis and PS3s of today are a dying breed with perhaps another cycle, maybe two, left in them. After that, it is anyone's guess. I believe that "portable" gaming will probably take the lead as the highest grossing/medium with the largest audience, but until those things reach power parity with a desktop, when they can handle games of the same scope and size, I don't think PC gaming is under any threat.