I think the reason that some Rolling Stones songs do resemble some songs released in the solo albums by certain members of the band is that in both cases the songs were written by the same person. No racket science.
OpenG, I don't claim that your theory is not true. SOL can be a filler from a Jagger solo, but I don't think it is a filler in the context of a Stones record. Usually people don't release fillers as the first single of the album. Jagger seems to direct his most ambitious ideas to his solos (don't need to fight with Keith?), and retain the simpler and more conservative ones for the use of good ol' Stones.
- Doxa