Dmitriy Sintsov wrote:
because in MediaWiki it's interchangable with the space character. The type of the document should be determined by it's mime-type. If Google uses the web path "extension" (which is meaningless by the way, because that's a virtual path) instead of mime-type to determine whether the page should be indexed, that's amazing bug for Google.
It's a necessary evil however, because of a number of servers that serve incorrect mime types. IIRC, previously Google didn't index our images at all, but later added MediaWiki as an exception.