The circumstances are very different. Essentially Buffy has decided to charge for her Slaying activities (funding her army that helps humankind), but she's not upfront about it the way Angel was. It's like... Angel saving someone (rich) because it's what he does, being a hero and all, and then breaking in and stealing from that person when he needs to pay the bills.

(Basically Buffy is proactive, whereas Angel in S2 was reactive. That's the difference.)