Well, I'm going to give this a shot. Any chance the store you visited was a corporate store or a 3rd party store? In my area there is 1 corporate and 2 3rd party. I believe the corporate stores' employees get better training than the 3rd party. The 3rd party store where I live doesn't even know where the T-Mobile cell towers are located!
I have seen this happen in a few stores I frequent. Unfortunately, T-Mobile doesn't do enough to deter its employees from deceiving customers and store managers don't regularly meet with employees to keep them informed and up to date on the things consumers expect them to know. This is a change the needs to come from the CEO's office and quickly makes its way down to the store level.