Já vi a MS usar muitos servidores BSD ou Linux, principalmente antes do lançamento do Windows 2000. Isso não seria novidade, não seria a primeira vez.
Eu mesmo resolvi rodar nmap e confirmo a informação. É mesmo Debian, vejam:
ktk@ktk7:~$ nmap -A -sV www.inkblotpassword.com
Starting Nmap 4.20 ( http://insecure.org ) at 2007-12-08 11:51 BRST
Warning: Hostname www.inkblotpassword.com resolves to 4 IPs. Using 67.202.22.224.
Interesting ports on ec2-67-202-22-224.compute-1.amazonaws.com (67.202.22.224):
Not shown: 1693 filtered ports
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 4.3p2 Debian 9 (protocol 2.0)
25/tcp open smtp Exim smtpd 4.63
80/tcp open http Apache httpd 1.3.34 ((Debian) mod_python/2.7.11 Python/2.4.4c0 mod_ssl/2.8.25 OpenSSL/0.9.8c)
443/tcp open http Apache httpd 1.3.34 ((Debian) mod_python/2.7.11 Python/2.4.4c0 mod_ssl/2.8.25 OpenSSL/0.9.8c)
Service Info: Host: inkblotpassword.com; OS: Linux
Service detection performed. Please report any incorrect results at http://insecure.org/nmap/submit/ .
Nmap finished: 1 IP address (1 host up) scanned in 59.012 seconds