I think there is plenty of evidence to show that petitions do work.
Will a petition save HD DVD? Maybe not. Ultimately it comes down to sales. If inexpensive HD DVD players continue to sell then studios will make HD DVD. You want HD DVD then buy HD DVD.
It might look like BD has it all locked up, but the fact is only 1% of consumers have purchased a HD player in either format. I just don't see millions of people lining up to buy $400 BD players. Oh sure the PS3 is padding the BD numbers early in the game, but PS3 is dead last and at the very least the PS3 will lose the USA to Wii and Xbox 360 this generation. PS3 is the number one BD player by a long shot, but only a small percentage of gamers and Sony fans have purchased one. The gamers are not really buying PS3 for BD movies it is just another PS3 feature that may or may not be used. The CEO's that have made all of these exclusive BD deals are not price sensitive like your average consumer. Cheap upscaling DVD players outsell both HD formats by a long shot, and the DVD movies are cheaper too. If consumers were really smart they would tell the studios and manufacturers to keep both HD formats until they are really competitive; oh wait they already are.
The fact that we are here debating this means we are "bleeding edge" technology buyers, but we don't represent the mass market. I know exactly one person with a PS3, and his entire system has Sony labels on it. I know zero BD owners except for the PS3 owner. I know zero HD DVD owners. I know at least six Xbox 360 owners, and a few Wii owners that were lucky enough to find a player to buy. Most of my friends and co-workers haven't even purchased HDTV yet. I wouldn't call a winner based on what I have seen.