It wouldn't be surprising if the 240 mile range battery and the 220 mile range battery are actually the same part. (As I understand it, there is a trade-off between battery wear and what voltage you change and discharge to. So, the people with the "low capacity" battery may benefit by having a somewhat longer overall usable battery lifetime.)
If that's the case and the "bigger" battery costs nothing to Tesla, the $37k version has a higher margin if the enhanced interior features cost less than ~$2k.