1. On2 never went to market with VP8 before the sale to Google. To say that they weren't sued for something they didn't release doesn't prove anything, especially since VP8 was marketed as a evolution of VP6.

2. See #1, they licensed VP6 not VP8/WebM.

3. No doubt!

4. Google does not indemnify users of WebM (http://www.webmproject.org/license/software/). If someone were to sue you for WebM, it's not an attack on Google and they have no reason to pick up your legal bill. Sure, it's not unreasonable to assume that if many large companies adopt a technology it's safe to use, but it doesn't protect you from being attacked individually.

Armchair legal hand waving goes both ways.