Safari and Internet Explorer only support H.264. Chrome, Android browser and Firefox support H.264 (FF on Linux & Windows IIRC).

H.264 doesn't just get to iOS devices. It's the only way to make sure your web video shows on ~98% of all devices.

It's not just iOS. It's PITA to upload videos to Commons for an ordinary person. It's a legitimate problem. That said, list of unsupported _free_ formats: https://commons.wikimedia.org/wiki/Commons:UNSUPPORTED No 3D, no raw, no CSV, no HDRi, no JPEG2000 (widely used by archives), etc. Or even H.261, its patents probably expired already, and it's widely used by various archives. But very little happens in these directions.

Not just iOS. Almost all devices these days have hardware encoding/decoding for h.264. Webm and ogg just don't have that level of penetration. From strictly an experience standpoint (disregarding the politics of it all), h.264 will give users a better experience pretty much across the board. All of nvidia’s kepler-class GPUs have dedicated h.264 hardware. Both Intel and AMD have GPU accelerated solutions for h.264.

For ogg and webm, not so much. I think it's smart that wikipedia is discussing moving to this, as it'll make it more accessible.