reason being: thermal receipt printers have higher uptime with lower maintenance costs, they print faster, and use no consumable other than the paper.
at my office we don't print many receipts, but we use plain paper (letter, half letter or photo paper sized--as appropriate) loaded into a normal inkjet printer that uses cheap (~ $2 ea) knockoff ink cartridges that get recycled (we hope, anyway, when we drop them off at a collection point).
harvard has a hell of a lot more than just the largest endowment of any educational institution.