The first month is where games often see the most sales, so if Green Day sold around 80,000 in that period, we can extrapolate that it probably sold close to 200,000 in total, and that's if we're being generous.
Now, I don't claim to have complete insight into the development cycle of GD:RB, but it's fair to say that it would have cost a fair bit more money to license and accrue the materials required for making the game than any old DLC pack, or even the previous GD packs. The game had three full albums (more or less), split across a few different labels, in itself adding to the busywork and cost of the game. Given that there was still one track missing from Dookie, and it was revealed that digitizing the previous two albums woul destroy the masters, it should show that the acquisition of the masters they did get was definitely harder than the average song, though still not nearly as difficult as The Beatles, of course.
Add to this the general development cost of a full band game (mo-cap, old materials and extras, revamped interfaces). But we're not done yet. Here's the biggest seperation.
For selling DLC, Harmonix only needs to split the profits to one party each: Microsoft, Sony and Nintendo, for hosting the DLC on their online services, and I stipulate that all they do is take a portion of the money made from a sale of a DLC item, similar to how Steam purpotedly does it. With a retail game?
Again, I have no inside knowledge into HMX's business deal with EA, but they sure as hell weren't going to let them have all the profit, especially when they had to ship and distribute it themselves. Add to this the cost of retailers holding onto the game and it's hard to say if HMX saw much money back on each sale of the game. And again, the cost for distributing a retail title is expotentially higher than distributing DLC, even if you're handing the job to someone else.
I did some quick math, and if we were to assume that GD:RB sold for $45 RRP, if we multiplied that by 80,000, the number of units sold in the first few weeks, you'll see that the money generated what $3.6 million. If we take that to 200,000, we come up with $9 million. That's paltry, pure and simple.