MS are catching up though, I can't remember the stats but 5 years ago I think 90% of servers were to Linux, now its more like 60%. I do think Linux/Apache/PHP is more stable than IIS and ASP.NET though.
I don't think your stats are particularly accurate. Unix variants (as opposed to Linux in particular) accounted for the majority of web servers - not to be confused with 'servers' in general, but I believe the figure was arguably fairly close to half of all web servers. W+IIS accounted for the majority of the remaining half, though the issue is clouded by the possibility of running Apache on Windows (don't forget that these surveys usually consist of a mixture of specific sampling from a reduced population (as per TV viewing figures) combined with actual statistical sampling (most probably reading HTTP header strings, which would result in some false positives for Apache).
Additionally, you fail to account for the majority of corporate intranet servers which are IIS based. I know we have a drive toward a huuuuge investment in IIS-based W2K3 boxen, even though the odd rogue LAMP box exists (normally as a result of 'someone going it alone (good on 'em)').
Anyway, LAMP isn't necessarily any more stable than W2K+/IIS, despite my earlier arguments that the desktop Windows offerings are unreliable. I've been running my own dedicated web servers since 2000, originally NT4/AS+IIS, now W2K/AS+IIS, and they have been rock-solid reliable. WHich points to Windows desktop apps being uneasy bedfellows in the reliability stakes.
FWIW, I think Apache is where it's at, but I am more experienced in developing for, and working with, W2K+/AS based IIS infrastructures, and I personally find them very dependable. In terms of security, well, that's well publicised and I reckon most security breaches are a result of users' interactive use of Windows machines, rather than direct hacking as such (assuming that any server is living behind at least a basic firewall, and has ports locked down and the latest MS patches).
The desktop Windows OS', on the other hand... well, I don't want to get back into my wrangling with my good ole buddy Greg on this point. Let's just say that I think Windows in general has a way to go as a 'user platform' whilst their Server products are a lot better. Security concerns to one side, of course - but that's also true of LAMP, just not so widely publicised.
I will shortly be regaining possession of an old web server (W2K/AS, dual Xeon 3GHz, 2Gb RAM, 15K SCSI U320 drives in RAID 1) which I intend to turn into a LAMP box. Probably...