Thats the standard Canon offer that all the sellers have. It is usually restricted co certain DSLRs, and not all cameras as you imply. There is also a rebate for the Pro 9500 MK II.
The offer has been available for as long as I can remember, the printer model updates when new ones come out.
If you need a printer, its a good deal. If you plan to get the free printer and resell it, everyone else seems to have the same idea, Craigslist is plastered with hopeful sellers.