Maybe for people new to dSLRs.
OTOH, I know Nikon shooters who appreciate the variety of Canon lenses (and availability of rentals), and I know Canon shooters who appreciate the low noise, high ISO shots that you can get from the new Nikons (this includes me
). But I don't personally know any Nikon or Canon shooters who are likely to be tempted away to Oly or Sony or Pentax.
There are a non-trivial number of folks who switch brands, I'd hazard a guess that it may be as high as 5%. Most of those people aren't very good photographers and they switch thinking the newest body from whatever manufacturer will "fix" their lack of skill- DPR is full of posts that prove the point. If Sony were to pick up say 2-3% of the market that way it wouldn't be a big deal, but if they got volumes going enough to take that 5% and an additional 2% because they got enough momentum, then there'd start to be a shift in the balance- and that doesn't take into account the fact that DSLRs are still a growing market- so those new customers really do matter. When we eventually hit market contraction, then having some of that momentum may be the difference between floating and sinking- especially the way prices are going at the moment.
Don't forget, lots of the new folks want video- and Sony's got a lot of experience and development already tied up in video- so long as the Handycam and Alpha folks don't get into turf wars (Handycam will win) Sony probably has as much chance of interesting innovation in the emerging part of the market as anyone- and they've got a distribution channel to match.
But the fact is that Canon and Nikon don't do head-to-head- I doubt that upsetting the balance is a primary reason, but it's a great side benefit.
Neither company can afford to be complacent- and signs are that they're not being so. If the others weren't blundering around so much, it'd be even more critical- but losing share in a growing market has been bad for Pentax and Oly. Sony's fudging numbers to try to claim growth targets a couple of years ago was sad, but I think they're the one to watch- I don't think they hit their ~15% projection, but I think they probably came up over 10. I also don't think those are predominately old Minolta shooters.
