> WebM is not a standard. [...] This does not make it a standard.

While not being a de jure standard it may become a de facto standard.

http://videojs.com/2011/01/html5-video-statistics/

> not good for commercial software.

MKV support is offered by both commercial software and commercial hardware:

http://en.wikipedia.org/wiki/Matroska#Software_support
http://en.wikipedia.org/wiki/Matroska#Hardware_support