Binding contracts are binding.
Being cranky about something isn't grounds to break a contract, but it could be grounds not to sign one. If the ink on their contracts was dry before Nissan hit the track with the GT-R, then there would be nothing Porsche could do about it (unless the language in their contract granted them some sort of creative veto right, or option to back out). And besides, it's not like EA is in bed with Nissan, the same way PD is. It could be about more than just the 'Ring time.
Since the 'Ring fiasco, have you seen Porsche and the GT-R added to the same game, that you know for sure they signed up for after the fact? I would wager a guess that both Nissan and Porsche were already on board for Shift, or that Porsche was already bound by their contract, and helpless to influence the developers with which they already had contracts... which would make them more apprehensive to signing any further agreements.
Maybe EA didn't buy Nissan's 'Ring claims, and the GT-R in their game is more representative of what Porsche and the rest of the automotive world have achieved with the stock GT-R, and what their physics engine says a car with that weight, power and grip, should accomplish. Whereas we know from Kaz's interview with the GT-R's test driver, that PD used their Nurburgring demo model to run a near-perfect lap, since he had mentioned a wet part of the track that may have cost him time, which means the GT-R in GT is capable of the time that Nissan claims the real stock car is capable of.
Maybe Porsche doesn't see EA, and the NFS brand as serious a sim as GT.
It's all valid. Why? Because we are all speculating. None of us work for Porsche or PD, and neither company is saying much. To be a fly on the wall...
Like I said, it could be a factor. I'm not here to convince anyone that it's gospel, just opening up some possibilities.
I can't believe it would be just about the money when it comes to the premiere racing game, and one of the Playstations all time best selling franchises. How much money can they want? And why haven't they asked me if I'll chip in? Though some vocal few will protest DLC, most of us will pay if we have to, to get a brand as significant as Porsche. Many other games have proven that DLC and micro transactions are immensely popular, and Porsche and PD would be stupid not to get in on a gold mine like that... unless of course there were some petty differences they couldn't overcome... Maybe they're just buttering us up for exactly that...