People who say "The technological difference between PS3/360 and Wii will prove so bad that in a couple of years the Wii will be dead" are probably the same bunch who made the exact same bold comments with regard to the DS and the PSP ("Once Sony unlocks 333MHz, the technological gap will be too much for the gimmicky waffle-maker"). As of now, the technological gap is already wide enough to affirm that it doesn't count.
Regarding Japanese devs, they are looking at the same figures as we are, and they have two alternatives to remain profitable : first one is to make the kind of games aimed at what the Japanese market wants now (quirky games, pachinko, "non-games", plus of course the various surefire hits of anime ports). In most/all of those genres, the added power of the PS3 doesn't mean much apart from added dev costs. Wii and/or DS are the platforms of choice. There are a couple of exceptions (Monster Hunter comes to mind), but not enough to sustain a company.
Second alternative is to open to the West, and make Japanese games that appeal to the Western tastes. And in that case, it makes no sense to develop exclusively for PS3, and ignore the 360. That's the road Capcom took. Because apart from a few high-profile exceptions, it doesn't look like the Japanese market can make a high-tech next-gen game profitable.
As it is now, it looks like in Japan the PS3 could end the Gamecube of this generation, with very slow sales and flares when a big game comes. At each of those surges, fanboys will come out of the wood and indicate this is the start of a pattern, and that the console is really finding its way, only to have it crawl back to its original position a couple weeks later.
The Wii is already 'obsolete' in technology. However, that doesn't matter when it comes to enjoyment.
