to be honesty with you, just because somethings water proof and has a faster shutter release doesnt make it pro, i know they sell it on their pro line but in all honesty it doesnt make it pro. so the general concensis is that its water resistant and has a faster shutter release, and maybe better metering...which can be over come if you know what your doing. hmmm seems like even if your a pro going for the d1x isnt a good idea.
hehe. Go to your local camera store and hold a professional series camera and you'll instantly know why they are pro level. Even the D200 weighs 29.3 oz compared to your Alpha which weighs 19 oz. May not seem like much, but that little weight matters in your hand.
If you have ever held the rebel XT, it weighs 17.1 oz and feels like a toy. The difference from my friends XT (even with the battery grip) to my K10D's 25 oz is really incredible.
Compare that to the D2Xs which weighs an incredible 38.4 oz and instantly you know that pro cameras are made beefier and more durable.
As for Canons pro line, you also get APS-H sized sensors (1.3x crop) or even full frame, which by itself is worth the cost.
Also, as far as metering, the fancy meters of pro series cameras IS important. Yeah, all you really need to get good shots is an accurate spot meter, but think about the pro who doesnt have time to make sure metering is correct and needs to snap a shot NOW, not in a couple seconds. Also the AF systems are advanced allowing for great accuracy of moving objects (wild animals, birds, cars, football players).
Does everyone need a pro camera? definitely not. Are the upgrades worth it to everyone? of course not, but the fact is pro cameras do have advantages over consumer cameras.