I saw this exact ad for the first time this morning. I'm not one to be offended by ads but this one did irk me a little - I'm running 10 Pro which I paid $100 for, I shouldn't see ads in a paid product.
You needed a licensed Windows 7 or 8 in order to upgrade; that one costs money too. You weren't able to get entirely free upgrade. It was more of exchange.
Again, not justifying the add- but I wouldn't be surprised if its because our accounts were at one time linked to home.