I expect that will be a common belief long after it ceases to be a true belief. There's still people that avoid PNGs because "they don't work properly in Internet Explorer" but most vaguely web-savvy people wouldn't bat an eyelid at a PNG today. I want the same thing to happen for HTML5 video: the latest version of every major browser supports it, including Internet Explorer, and including mobile browsers; the biggest limitation I can think of is forum software that doesn't yet have <video> on its whitelist, but time (and a bit of targeted complaining) should solve that too.