Butting in here. That's actually not really true. The game assumes you can take that many encounters before you're tapped out of resources. But there's nothing that says that the PCs have to use up every resource they have in a day. Nor, for that matter, is there anything that you have to stick to the XP budget. The DMG specifically talks about the XP budget being used to determine how many monsters to sic on the PCs, but that's less helpful if you give XP for social encounters, and utterly meaningless if you use story or session-based advancement instead of XP.