When MPEG LA first announced the VP8 pool formation, a rush of companies applied to be in the pool, partly because everyone wanted to see what everyone else had. That gave way to some amount of disappointment. And by 'some amount' I mean 'rather a lot really, more than the MPEG-LA would care to admit.'
Eventually, things whittled down to a few holdouts. Those '11 patent holders' do not assert they have patents that cover the spec. They said '_may_ cover'. The press release itself repeats this. Then these patent holders said 'and we're willing to make that vague threat go away for a little cash'. Google paid the cash. This is what lawyers do.
That's why it's a huge newsworthy deal when companies like NewEgg actually take the more expensive out and litigate a patent. It is always more expensive than settling, even if you'd win the case, and very few companies are willing or able to do it. Google was probably able, but not willing.
We deal with this in the IETF all the time. Someone files a draft and a slew of companies file IPR statements that claim they have patents that 'may' read on the draft. Unlike other SDOs though, the IETF requires them to actually list the patent numbers so we can analyze and refute. And despite unequivocal third-party analyses stating 'there is no possibility patent X applies', these companies still present their discredited IPR statements to 'customers' and mention that these customers may be sued if they don't license. This is not the exception; this is standard operating procedure in the industry. These licensing tactics, for example, account for more than half of Qualcomm's total corporate income.
It's this last threat that Google paid a nominal sum to make go away. It's the best anyone can hope for in a broken system. If those 11 patent holders had a strong claim, it is exceedingly unlikely they would have agreed to a perpetual, transferable, royalty free license.