You're probably talking about some specific console-games, that is, in your experience suited and designed for a game-pad, which is pretty much inherently a proprietary device.I can give you a few example that the gamepad trump mouse+keyboard easily, like it's hard to imagine playing Ninja Gaiden with a mouse and keyboard, if being simpler is all what the gamepad is, then mouse&keyboard should be able to handle that game with no problem ... which they don't. Also don't underestimate the precision of good console .
When you for example want a more realistic game, like say, FSX or any *decent* simulator (we're talking about in relation to the real world), you definitively should buy a proper joystick and still use the keyboard and mouse, at least you have your own freedom to choose any of these three items independently of the brand, fitting your specific preferences.