I think the worry was actually, "Isn't my data backed up somewhere even if you delete it the instant I tell you to? So then you still have my data?"

bingo. If they can delete my data on the instant -- then they quite possibly don't have backups. If they do have some form of semi offline backups - then not all of my data is deleted on the instant.

Not a worry so much as a harder problem that sometimes doesn't get considered.