CentOS in the top500 supercomputers

Browsing through the top500 supercomputers list, I noticed that in the OS listing, 5 supercomputers are running specifically CentOS (1%) while 389 are running some sort of Linux (not specified).

From the Linux list undoubtedly more are using CentOS, but the remarkable fact is that this known 1% CentOS is the same amount as the 5 Windows supercomputers.