They offered patent indemnification from patents that 'Google' holds. That's nice, but that doesn't protect you from the patents that anyone else holds. H.264 has been around long enough that it is unlikely their are anymore submarine patents out there (or if there are, it is likely they can brought into the patent pool). Also, Microsoft has agreed to indemnify any user using H.264 on their platform. Google refuses to do the same for WebM.
Software patents are evil, but they are also very painful if you are the one sued. Personally, I would rather deal with the devil I know than the devil I don't.