I think you're confusing what *you* want a server to be with what other people might want it to be. Cheap and efficient are nice, but there are other factors which *in a given situation* might over-ride these - lower admin overhead, current skills set, existing infrastructure - you name it.
Case in point - I'm involved in a project putting lots of servers out at small sites to do some network monitoring - MRTG, NTOP, web caching, DNS, file storage, print serving - the gubbins. Clients are Windows 2K/XP and will have to remain so because of some of the software they're running, and because with our support ratios we need tools like SMS to manage stuff. I built identical servers on both Linux+Samba and W2K3. W2K3 won, even with the licencing cost. The reason was simply that the W2K3 version, *with our current skills set*, was far easier to manage, troubleshoot, configure and implement. It was also slightly faster on file and a lot faster on print, on comparable hardware. That's real world, neither MS evangelist nor Linux evangelist.
It is time for the OS wars protagonists to grow the hell up. There is no "best" for everything. It's not even as if one platform is *always* the best for a given application. There are too many other factors to consider.
If you want my prediction (and who would), I think MS is going to get friendlier towards Linux (we've already seen this with the MS/NetWare deal). MS know what I've said above, and they know that savvy engineers will want to use a mixture of stuff according to requirements. The better their stuff integrates with other peoples', the better they can maintain a position in the server room. The are, I think, beginning to realise that their dream of a world of MS only shops just ain't going to happen.
Paris, because she is too thick to get involved in OS wars, as opposed to those who are clever enough to do so, but not clever enough to see the silly tribalism for what it is.