If this type of thing happens and it's accepted, what's stopping for example the Ilitches from saying "sign in Detroit and Little Ceasars will give you an X million dollar sponsorship"?
Well to start Stamkos already has a deal in place with Sportchek (owned by Canadian Tire) so the Leafs aren't negotiating or introducing him any new sponsors.
Mike Illitch would clearly be circumventing the cap.
It is beneficial for companies like Sportchek to have Stamkos in Toronto. They would have Steven Stamkos related products everywhere.