timppu: I agree having a default setup for PC gamepads is a good thing, but I don't recall it being that messy in the DirectInput era either. Back then, almost all PC gamepads seemed to mimic the PS2 gamepad design, even by the coloring of the buttons etc. Now they are all following the XBox360 gamepad design, more or less.
In terms of form factor, yes, most emulate the PlayStation gamepad.
The catch comes with the button layout. Some joypads are missing buttons under the sticks, some have only two trigger buttons, some have six buttons on the face, some have no start and select buttons, the list goes on.
Not to mention that some joypads change the layout of the four face buttons. Some have button 1 on the bottom and button 2 on the right, some have button 1 on the left and button 2 on the top.
As long as the game allows the controls to be reconfigured, this isn't a problem, but if it doesn't, it can cause some major problems (Rayman 2 anyone?)