With few exceptions, any time a developer has truly taken the time to put the effort into making a truly great game on either the Wii or DS, it has gone on to become a success in time. Madworld's closest relation on Wii are the No More Heroes titles which also started slow and eventually became quite successful considering their relatively small budget.
As for GTA:CTW. There hasn't really been anything like it on DS before so it's going to take time for handheld gamers to discover it but eventually they will. Didn't GTA3 on PS2 start off slow before eventually becoming the mega-hit we remember it as?