[ShardPhoenix]

How do they even tell, given that sites can avoid having .php/.asp/.jsp in their URLs if they want to?

[sucuri2]

We checked the extensions, the "Server:" option in the header and the "X-Powered-by" option. We tried our best:)

[th]

So were the other 68.7% all unknown?

[sorbus]

Well, given that those stats add up to a lot less than 100%, one assumes that they cannot in most cases.