Post office employees, the counter employees, actually do a fairly difficult job and they do it pretty well. They have to know tons of stuff, rates, postal regulations, types of service available. They have to have customer skills. They are unionized employees and they probably average over $20-an-hour in pay, often get regular overtime (working Saturdays), have an excellent benefit package and have a career path that includes promotion to supervisory positions (if they want it).
The model for Staples employees is more like the fast food industry. They're not unionized, and they get minimal everything: minimal pay ($10-an-hour), minimal benefits, minimal training and few chances of advancement.
I'd be very surprised if Staples will be able to offer the same quality of service. It's hard to be motivated when you're making ten bucks an hour with no benefits. I use Staples too; I publish a small newsletter and I use the Copy Center regularly. The employees are friendly but the level of professionalism is more like a McDonald's than a post office. The Staples employees are, for the most part, much younger and much less disciplined. It's normal to have to wait to be served while being ignored by several employees chatting among themselves. I've never had that happen in the post office.