You know, for the most part, I agree with you. There is really only one argument, when talking brands, that really should tip the balance toward Canon or Nikon, in my opinion.
Stability.
Canon and Nikon are both solid as a rock. Neither of them is in danger of disappearing.
Brands like Minolta would scare me personally. Sure Sony isn't going anywhere, but all it would take is a few bad years by the Minolta brand and I can see a corporation like Sony shutting the brand down or selling it off to some wild card third party.
As highly unlikely as that might sound to you, as a professional, I need to know that my equipment manufacturer is going to be around and solid for as far into the future as humanly possible. I wouldn't feel that comfort level with Sony calling the shots.
On an unrelated note, I buy 99% of my equipment from B&H. They have everything you can imagine, ship quickly, and have always stood behind their merchandise if there is a problem. Plus, their web site is well designed and easy to navigate.
I agree with you, but I feel that Sony has as good as Stability as Canon now.
Minolta
IS gone, they sold all their design's and technology to Sony, so I now shoot Sony bodies with a lot of old Minolta glass.
I would personally say that Sony is safe, as well as Canon and Nikon. Sony has a MASSIVE consumer electronics division to keep it going, and have done really well in gaining market share that Minolta never had. Like I said both Sony and Nikon have been eating away at Canon.
check it out:
http://www.photographyblog.com/news/dslr_market_shares_gainers_losers/http://www.photoscala.de/Artikel/DSLR-Welt-im-WandelThe only thing Sony is really lacking now as far as a Pro system is the support (fast service centers, lens rental availability, etc) but that is growing too. I know of at least half a dozen well respected pros shooting with the A900 now.
Pentax and Olympus, I have now idea what their long term stability looks like, but I hope they make it, more competition is always better.
Sigma (camera division, not lenses) and Fuji both going down the crapper I think, wouldn't touch them with a ten foot pole.