If You Could Have Changed 1 Thing in Each Console's Release, what would it have been?
Wii - Add Wi-Fi with Wii Sports
PS3 - Remove SIXAXIS and add Dual-Shock 3
360* - Noise! Make the console run cooler and quieter.
As for DS and PSP, I really don't know much about them, so I won't set an opinion, although feel free to do so!
*I would have said "Fix the RROD!" but these types of things are set by percentages in each console, so there was no actual way MS could foresee the RROD. I guess one could say "test your console out more!".