I think I have a handle on this now.
Seems to me the only significant design differences are:
1) Whether friend codes or whatever are persistent outside a particular game
They are on PS3 and Xbox 360, but are not on Wii. this would mean that on the HD consoles you can keep contact with people outside of a particular game/keep friend lists outside the game environment/see what people are doing/compare scores and so on. Whereas on Wii you have to keep swapping friend codes with people for every game you've got.
2) How you meet people
You can meet people online and befriend them that way on PS3 and Xbox 360 but not on Wii where you have to make contact some other way first (except maybe on MK Wii?)
3) Whether there's a public forum (for want of a better term)
There is for PS3 (Home), but there isn't for the other two.
The rest of it is all down to content/reliability and the sort of people you meet.
Is that roughly it?







