Commutativity of addition is not at all an obvious fact and I applaud your erstwhile employers for holding you to a higher standard of rigor.

Maybe it's just me, but I find it difficult to conceive of someone to whom, even after discussion and contemplation, (+4+3)=(+7) is not obvious. I suppose there are such people wandering the planet, however.

Nitpick: the property observed here is associativity(sp?), not commutativity.

Was there a reason why they did it that way? And did you have a reason to find it lacking?

Yes, there was a reason they did it that way. They were unable to comprehend that +4+3 = +7.

I found it "lacking" because it was tedious and exasperating to stand there with a little pocket calculator adding 4, then adding 3, to make price tags for hundreds of items, one at a time.