I think making us purchase happy, while indeed very beneficial to the owning class, is still just a side effect (E: of the length of the work day, not capitalism in general) to the real reason (and why the 8 hour work day is a compromise people had to fight, and die, for) - keeping us tired and hungry (and not only for indulgence) and at risk of losing it all if we don't go to work tomorrow keeps us from having the time, energy, and community (because capitalism encourages crab mentality) to organise and revolt against them, and their oppressive systems.