As a guess it probably takes 33% to 66% as many developers 50% to 75% as long to make the kinds of games you listed than a game like Spyborgs or MadWorld ... Now, given similar resources this would translate to 2 to 6 times as many of these smaller games being released (or announced) in the same timeframe.
Personally, I suspect the success of the Wii has translated into developers realizing that not everyone wants the experiences they have offered with the HD consoles and they probably are focusing on creating different kinds of games on the Wii. I do think they are working on more conventional big budget games, but with how long these games tend to take to develop and how few they can develop at a time they will never make up the bulk of most third party publisher's line-up for the Wii.
