How about using all colour schemes and let the user change the colour scheme on the fly... the best of both worlds! I'd assume websites use those colours as they may look more professional with a similar colour scheme to microsoft or maybe it's earthly coulours - greens and blues?! That's probably of no help to you - good luck!
There might be a psychological effect (it is quite a soft and relaxing color, isn't it?), but it might also be that Microsoft just wants to show they are making "brand new" products. You can follow the hype, or decide for yourself what color you want.
(PS: I'm not a web designer, just a plain user)
I think this is just a trend. Green and blue are both relatively cold colours but combining them still creates an illusion of colourfulness - not too cheerful like pink or orange but still not depressing like a plain white or grey page.
I doubt there's much in it really (but if you talked to a psychologist or a designer I'm sure plenty of "reasons" would fall out).
Site designs come and go in trends. A while ago rounded corners were cool, now it's faded blocks. White used to be in, now it's passé.
I remember reading an article that described how aspirin sold more when the label was a shade of blue similar to the image you posted; supposedly it’s calming.
This site http://colorschemedesigner.com/ is a nice way of creating a complementary colour scheme based on well tried principles. I’ve used it several times to good effect.
T'is web fashion. The popular sites parade down the tubey catwalk and show off their latest crazy inventions and the rest of the world follows suit with cheap knock-offs. The popular ones don't like being copied so they change.
Specifically though, it looks a bit like the sea. I'm not sure what the psychological effects are. Maybe it's a Microsoft Conspiracy(TM) to make everyone buy Vista.
there might also be an effect that the small fishes (unconsciously) copy color schemes from big successfull companies because you get success associated with this design!