I can not ping microsoft.com but can open it through Firefox. I am using 12.04LTS. I am able to ping all other websites.
In this particular case, microsoft servers blocks/drops ICMP packets and don't reply to them at all. For such cases is better use other tools like nmap to have an accurate result:
nmap -p 80 microsoft.com
Starting Nmap 6.40 ( http://nmap.org ) at 2014-03-03 13:08 AST
Nmap scan report for microsoft.com (65.55.58.201)
Host is up (0.14s latency).
Other addresses for microsoft.com (not scanned): 64.4.11.37
rDNS record for 65.55.58.201: 00001001.ch
PORT STATE SERVICE
80/tcp open http
Nmap done: 1 IP address (1 host up) scanned in 0.65 seconds
As you can see the "host is up" even through it doesn't answer the ICMP echo packet.
