I never had a tiered cake except at a wedding either, but all of that was before cable, before Food Network, before Duff Goldman.
It's education time, folks. People order sheets because they are USED to ordering sheets. Like when they ask for a "half sheet" to feed 10 people. They use the terms because it's habit. It's what they've always done. It's all they know.
My non-wedding sheets are cheaper because I dont' deliver them. I don't have to close the store; I don't have to drive anywhere. I'll happily do them because they help pay the rent.
I'm not rich enough to be particularly snooty about the shape of the cake I decorate.