[Kers]

this line explains what you're asking about i think:

But, But, you didn't say anything about the penalties when you talked about how xp is split!!! why not?

When the tasty pie is cut into slices for the group, the levels of the various PCs are not consulted (not directly anyway), only the xp totals for the PCs. The game code doesn't care if Bob is a human or an elf, a bard or a monk, level 10 or level 15... the game code only cares what Bob's total xp is.