There was a thread here last year about someone who ran into that with his (presumably BofA?) Worldpoints
card. A quick look at the Googles has a bunch of other BofA cards (Norwegian Cruise
) with that phrase in the fine print, as well as Barclaycard
and various others.
I do think it's probably more of a "let's put this in here so we can close down the card if we don't like the way it's being used" thing. I can go spend $5k at a home improvement store to redo my bathroom, or I can spend $5k at a home improvement store to renovate a rental house for my biz... they won't know the difference. But since "let's go spend $_k on gift cards at the Office Supply store" (or grocery store, or WalMart, or wherever) is a classic points-churning strategy, it gives them the opportunity to say, "Hey, these aren't normal spending patterns for normal people. We think you're using this for business, and that's not allowed."