Nikon have regularly updated their pro level bodies, the D2 was followed by the D2x and the D3 by the D3s, this has kept the product line fresh and also given them new sales as users trade up.
By contrast the 1D MkIII badly in need of a refresh has had disspointing sales, yet a refresh with a new higher resolution screen, the improved sensor from the 5D MkII might just have added something to a product which is looking very tired. It's not as if the changes would have cost much to implement, they're already in the parts bin, in fact the standardisation of both lines might actually have saved money.
I have a couple of issues with this:
1. if you get in a habit of releasing mid-cycle refreshes ("N"-type bodies), people will come to expect them. that sets a dangerous precedent (from a moneymaking perspective). 3 years is a long time to hold out, so people who need something close to that will bite the bullet and buy. 1.5 years is not such a long time to hold out, so you'll basically have folks that keep pushing off their purchase in the hopes of something better soon to come.
2. I applaud canon for not taking a "parts-bin" solution to any of its top-line bodies. these are cameras that canon invests heavily in to build from the ground up (especially the flagship camera) and that's precisely what we're paying for. I'd feel totally gypped as a consumer if canon were ever to pull what Ford did when they purchased Jaguar, releasing supposedly premium luxury vehicles with plenty of poorly manufactured bargain-bin parts (door handles on the ford jags, anyone?)
at the end of the day, however, Canon does have to produce the goods. if they make us wait this long, AND the specs on the new cameras are subpar to what nikon and sony put out ... well, general furor would be justified. but at the time being, our own impatience has nothing to do with the astuteness of the canon business model. I think they're playing this release cycle very well, and I too am looking for a trump-Nikon type of play to happen in September or October.