RE: To initiate a change (by those at fault) would be an admittance that what they did was wrong or misguided. Maybe pride is in the way. 

Yes, that would mean losing face. Can't have that!

RE: Or maybe they actually believe they know more about their customers' needs than their customers know.

Well, clearly they think you don't need functional invoices like QuickBooks Desktop has. That'd be way too much for you to handle. And probably wouldn't work well on a phone. 'Cause, you know, that's important.

RE: Either excuse is inexcusable.

Yea, but they're simple and work well on your phone!  You know, because using a phone to do your accounting is the wave of the future. Soon everyone will be doing it!