Think about it. Blink-182 broke up and everyone went on to do their own things (Boxcar Racer, Angels and Airways, +44 and so on) and were all successful within their own, but nothing could match what they had accomplished together in Blink. I'm certain no one in Blink-182 needs the money, but regardless if someone approached you and said "Want to have 3x more money and be super famous again?"...The obvious response is "Yes, yes I would like that very much". Even though Mark and Tom hate each other (you know they still do), they are all gonna get back together, put out an album, sell millions of copies and sell out arenas for shows. Sounds like a solid plan to me.
Same goes for No Doubt. Gwen goes off and does her own thing (Remember that Hollerback Girl song....Ahh I get shivers thinking of it...thank god shes getting back with ND) and is super successful. But when she gets back with No Doubt she will do much better, as will the rest of the band. These bands are realizing they can go back what made them rich and famous in the first place, and get rich and famous a second time around.
Now think of this. When System of a Down broke up (excuse me...went on Hiatus), everyone did their own thing...but no one was really successful. Serj did a solo album which, in my opinion was not all that bad (Empty Walls is an awesome song), but it didn't sell all that well. Daaron and John did Scars on Broadway which was a total failure, and Shavo went off punching members of Mastodon in the face. I have a solution for SOAD to fix their, now boring careers; GET THE FUCK BACK TOGETHER. We are all aware that they intend to make music together again someday, no one is saying they are gone forever, but now is the perfect oppertunity for them to start it upn again. It is a win-win-win situation. The record label makes bank, SOAD gets rich and famous again and we, the fans, finally get new music and tours from our favorite guilty pleasure. I'm sure the members of SOAD see this trend of reuniting bands, and will hope on the bandwagon.
That is why, I will bet that very soon, we will hear an announcement regarding the return of System of a Down, and oh, what a glorious day it will be.