Well, when "Sakura no Hanabiratachi 2008" was released, DefStar
did a promotion: if you fetched all 44 posters, you would get a ticket for a special event. The posters were given randomly, one per theater CD, so you would have to be very lucky to get them all buying just 44 CDs. They scrapped the idea because it was against law. However, if you do a raffle where your chances increases as you buy more CDs, it is not illegal, which is what they do now.
By the way, one would think fans are abused by this, but technically nobody forces them to participate. Also, there is a whole economy around AKB48. If you buy one limited edition CD, you get a picture, which you can sell at Yahoo! Auctions for some money (for most of the girls there is always someone willing to buy it). If you collect BLT pics, they sell pretty well. I have seen some pictures being sold for over USD 500.
This Yukirin set of 130 pictures is being auctioned for over USD 1,000. You can't sell handshake tickets since they got your name, but special gifts like 2-shots are anonymous, and I have seen some of those sell for over USD 2500.
They end up losing some money, true, but when I turn left and look at my game collection, I realize I have spent over USD 5,000 in games that I no longer play, some that are even factory sealed still. And it is a small collection, since I have never been a real hardcore gamer, and that I don't have easy access to gaming shops being from Argentina.
It is pretty similar to what happened with Magic: The Gathering, I had a couple of friends who earned enough money to live without working by just trading, buying and selling, spending 10-12 hours per day traveling to different places to get the best offers.
Regarding their songs, they are idols who aren't really proficient at singing or dancing (which is true for most Japanese idol groups). Except RIVER, Beginner and UZA, all other songs could be classified as bubblegum pop. But that is just part of what they sell. They are "cheerleaders", and should be rated in their whole and not just their songs.