I am well aware that the DOS website does not require or even mention that ears be visible in the passport photos. However, I went to Walgreens and had my daughter's photo taken there, her ears were not visible, and there was no mention of it by the clerk. However, when I went to the post office to turn in all the paperwork, the photos were rejected...you guessed it, the ears were not visible.
Walgreens refunded my money no problem and were great about the whole thing. They said there was no requirement of ears in their training, etc. But she did mention that they received a letter form their corporate office recently stating that the post office seems to be rejecting more and more outside photos so they can make the $15.99 themselves. IMO, this is what is happening.

As for it being more efficient to do at the post office, I agree - if you are willing to shell out the extra money. It's more efficient for me to get my oil changed at the same place that I rotate tires, but may not be the cheapest place.

I would expose my ears (easy for me personally since I have no hair!) from now on so that you don't have the hassle, but I would still go to Walgreens to save the money.