@DBZ_universe: The characters are in character. IIRC, Buu rarely absorbed his opponents. Especially Kid Buu. Also, absorbing them isn't winning. it's cheating.
Buu absorbs quite a lot, its absorption a sort of defensive mechanism. (If an opponent is stronger than him, then he absorbs them.) (Kid Buu vs South Kaioshin, Kid Buu absorbed him.)
Only buu that didn't absorb was Fat Buu, I think.
In Character, all Buu's would use the absorption ability. (Besides maybe Fat Buu)