Is MPEG LA's "Call for Patents" for Google's VP8 a sign of weakness?

Yesterday, MPEG LA, the agency that licenses patents related to MPEG-4/H.264, issued a "Call for Patents" for Google's VP8 video codec. VP8 is the video codec incorporated in Google's WebM format, which Google is licensing at no charge. MPEG LA wasn't asked to round up potentially applicable patents by Google. Instead, MPEG LA sees an opportunity to make money, in much the same way that attorneys around the U.S. advertise on late-night television to find users of various medications or workers in particular industries who might have been harmed.

Update, March 3, 2011: PaidContent reports that the U.S. Justice Department has begun an investigation of MPEG LA's actions related to VP8 to determine if they violate antitrust laws. The article suggests that MPEG LA itself may not be the real target of the investigation, but rather, one or more members of MPEG LA who might have reason to sabotage Google's open video efforts. 

The interesting thing is that executives from MPEG LA have been claiming that VP8 infringes its MPEG-4/H.264 patents since last summer, when VP8 was first made available for free by Google. If that's the case, why do they now have to go out and find patents that cover VP8? Didn't they already know which patents were being infringed when they charged that VP8 was "undoubtedly" infringing their existing patents? And, if they examined their existing patent pool and decided that nothing they've got covers VP8, what are the chances that they're going to find anything now?

This move, which is being seen by some observers as a threat to WebM, looks to me more like a statement of weakness by MPEG LA. To this observer, it looks as though they don't think that they can prevail with their current patent pool, and they're desperately looking for a "submarine" patent somewhere that will stand up against court challenges.

I would have taken MPEG LA's threats much more seriously if they had filed suit for patent infringement against Google using the patents they already represent. At this point, Google is in a much stronger position than I thought they were.