http://www.comcast.com/About/PressRelease/PressReleaseDetail.ashx?PRID=782&fss=free%20wii
Comcast's page on the deal.
In my area there are two cable services, then of course you could have one of the satellite companies. The cable companies have divided themselves to separate areas of the city, this basically makes them monopolies over certain areas.
So, if you are in Comcast's area and are already paying for one of the two packages described or nearly paying for those services, i.e. you may not have their phone, but have Internet and cable already, then this is a no brainer. Sign the two year contract and get the free Wii.
There is nothing in that press release that says you must be a new customer, it just says you have to sign a 2 year contract.