I think I figured it out. Ever since this thread was posted (and running some numbers in Excel) -- I think the error may have been on the part of the winner. Let's break down what he posted above.
-- I was made to understand that a swap meant that I would be trading in my 70D,
So far so good
-- for which I would receive the proceeds, than be given a P90DL,
So he's giving his car back to Tesla, and banking the proceeds
-- I would receive the proceeds, than be given a P90DL,
So he's getting the proceeds from his trade AND the P90DL for free?? I think this is the basis of the error in his calculation. That's not an "upgrade" that's a "free car" (P90DL). [what Andyw2100 described above.]
-- but would be responsible for the sales taxes, doc fees, and any income tax on the value of the prize
He clearly admits and accepts that he'd be responsible for the sales and income tax on the value of the prize
-- Since the value of the trade-in was greater and expected to offset this, it would have been a swap
He's applying the $72k trade-in value he thinks he's getting for his trade towards the tax on the P90DL (unclear if he expected tax on the full value or the net trade value), so it's a wash in his mind, maybe a little left over after paying the taxes, maybe not.
But any way I run it, he *is* trading in his car, but he *is *NOT* getting the proceeds from the 70D, and he *is* paying the differential tax on the P90DL, which he acknowledges he'd have to do.
If I'm trading someone thing A for thing B, I don't expect the trader to pay me cash for A AND hand over B. I'd expect to trade A for B straight up, and then pay tax on the difference between B and A. The only question here is the fair value for A in order to minimize the taxes.
So yes, if he's willing to pay the tax on the value differential, then yes, I think he's going to be out some additional cash (to the IRS) to close the deal and do the upgrade.
So while Tesla could have structured it differently, I think the winner also had some flawed assumptions on how it was going to work. He's not getting a free car, he's upgrading his existing car.
-- Now I'm told that I swap my 70D for the P90DL, but I'm responsible for the $79K) difference between the new car (+ taxes/fees) and the trade-in value of my old car. This comes out to be roughly $30K in federal/state income tax.
Yes, that's exactly how it should work, although Tesla could have done/handled it differently (say, a 'retail' trade-in value for the 70D)
edit: Quick and dirty bottom line is that he gets a new P90DL for about a $15k discount after taxes.