You guys are all ridiculous. The sense of entitlement is sad.
First off, the whole track list and price has not even been announced.
Second, Green Day not being famous enough is an understatement.
Dookie - won a Grammy (Rock Album), went Diamond
Insomniac - went double platinum
Nimrod - went double platinum
American Idiot - won 2 Grammy (Rock Album + Record of Year for Boulevard of Broken Dreams), 5xPlatinum
Their songs have been in movies, tv shows, and commercials.
Their tours have sold out.
As much as I like Offspring, they have not even come close to the success of Green Day and they arrived with Smash about the same time Dookie was released.
Third... understand it is a business for Harmonix. They need to have shelf space at stores so people can get into buying Harmonix products. Rock Band 2 is most likely "bookshelf" at your local/national chains at this point. Faced out they might have Lego Rock Band and The Beatles. After Christmas, the Beatles will probably get the same "bookshelf" treatment at that point. Now look at their competitor, Activision on the shelf will still have Band Hero, GH:Van Halen, Guitar Hero 5, and DJ Hero; not to mentioned what else Activision will most likely drop by the time RB: Green Day will be released (date has yet to be revealed). We can add in all their bookshelf titles... GH:A, GH:M, GH2, GH3, GH:WT, GH:SH.
Fourth, remember you do not have to buy it. If the price ends up being the same as Lego Rock Band... Lego Rock Band gave us 45 songs at $60 (includes export) which comes out to about $1.30/song unlike $2/song on DLC.
Lastly, the RB3 vs RB:GD discussion... who says they aren't working on RB3... my guess is they have been working on it. Harmonix worked on the Beatles at the same time when they were releasing Rock Band 2, Rock Band: AC/DC live, Track Vol 1, 2, Classic Rock, Country, and Metal in addition to their PSP release. You get the picture... they worked on multiple projects at the same time. Again, I wouldn't be surpised if they haven't been working on Rock Band 3 for a couple months now.
To sum it all up... There will be plenty of fans that will end up purchasing it whether it is to just to export it or to just enjoy one of their favorite bands. It might not be for every one but you have a CHOICE to purchase/play it or not. The band is still relevant with a good following unlike Activision's choice in Van Halen. If I recall correctly, people were up in arms about Lego Rock Band and look how many of you are playing it now

... And more if I recall correctly, I remember seeing multiple posts here and in other places about how much they would want certain Dookie or American Idiot songs... well here is your chance.