It may not be like the iPod deals. I am guessing that software is cracked and illegal such as the ones on Ebay.
I guess if you want wild guesses you can ask on TSG.
Or you could just put your zip into their box and read the terms and conditions and help files. Or do a Google search and see what sites are carrying their offer. An Adaware run indicates they apparently dont put any spyware on your computer during an inquiry.
From doing those things it appears the software is almost certainly legitimate and the offer is as well. It also appears it would be almost a full time job to accept and manage the offers without incurring more cost than just buying the software. And it also appears that it would be extremely difficult to fulfill their requirements within the specified time period. It also appears that they submit a W9 to the IRS and you pay income tax on the free gift.
I wouldnt touch it with a ten foot pole. That doesnt mean the software isnt genuine or even that you might be able to qualify for it with a concerted effort. You will end up with credit cards and subscriptions you will have to cancel before incurring costs exceeding what you would pay for the software though.