Windows hosts respond to regular pings but not to an NMap ping scan.

I have a network consisting of a mix of Windows and Linux machines. I've noticed that when I do a ping scan of the network using "nmap -sn", the Windows hosts block the pings, and they only seem to respond if I do a stealth scan. On the other hand, I wrote a shell script to do a ping scan of the network using the actual ping command, and the Windows hosts responded to that. I don't understand why this is so. Why would Windows hosts respond to a regular ping but block a ping coming from NMap? Aren't they basically the same thing?