http://caniuse.com/#feat=webm http://caniuse.com/#feat=mpeg4
That's even more compelling when you remember that the only browser which had releases with support for WebM but not H.264 is Firefox and that's been phasing out for awhile: support for H.264 shipped in FF21 on Windows, FF26 on Linux and FF35 on OS X.
Unless you have a lot of Mac users who don't upgrade, it's probably not worth the hassle particularly since WebM doesn't compress as well as H.264. If VP9 ships that story could change if it delivers an advantage over H.265 compelling enough to get Microsoft or Apple to integrate it or the larger video sides to add it to their toolchain. For most places it'd have to be really compelling to be worth nearly doubling their storage costs.
I can probably find some links later. As I see no option to upload video directly I'm wondering if it requires an account, or whether it was their new(ish) GIF conversion process (IIRC some look like original videos though).