The issue is simply that a core gamer tends to play more than a 2-3 new games a year and the Wii is suffering from the fact that it is churning out 2-3 very good title every year and not much else.
So a core gamer ( or anyone that plays more than a few games/year) has to have a HD platform to get his fix.
And it's understandable from Nintendo point of view why things are that way.
It's unlikely that newcomers to gaming will purchase more than 2-3 titles per year so what Nintendo releases satisfy that part of the market...
Mass market is about lemmings and sheeps...
You only release a few titles and make it so that everyone wants those....