For the sake of the argument, that's how I understand the situation
1. The eMail
1.1. The contents of the "Porsche" eMail are quoted regularly, yet I haven't seen a post pointing to the original thread where the contents of the eMail were first posted.
1.2. Because publishing RL names is very evil, there's no info about who received the eMail nor who sent it.
1.3. As the sender of the eMail is unknown to me, I cannot judge whether this person was in a position to give a qualified answer at all, if he or she had all the information at hand or was indeed in a position to make claims towards the legal business affairs. This would make things indeed very simple, because either there is some info on the interweb about the person's function at Porsche. Or one could simply phone Porsche and try to get hold of that person. You get the idea.
So, in summary, the eMail is of no help as it can't be cross-checked.
If I disregard the eMail, I have to make (other) assumptions
2. Copyright law in Germany
An "exclusive" license means two things. (a) Party A has the right to use copyrighted material from Party B. (b) Party B agrees not to sell these rights to another Party C.
It does not mean, that Party A is in any position to do anything further with its exclusive rights. If the contract between A and B is breached by C, it can either sue B or C. But it can not grant C to use the rights from B.
So if C wants to use said copyrighted material, it has to achieve an agreement with A (they don't enforce the "exclusive" part of the deal with B) and B (to license the material at all, and probably a modification to the exclusive deal with A).
In summary, either way Porsche plays a major part in the affair.
3. Company culture, both in general and at Porsche
You have to understand, that internal business matters are hardly ever discussed in public. It's, mildly speaking, highly unlikely that Porsche discloses such information at all or in detail.
Furthermore, Porsche used to be a patriarchic "shop" deeply influenced by tradition, a no-nonsense mindset and a passionate rivalry between Piech and Porsche. They don't do funny.
When I said "I was there" I meant when NFS
orsche hit the shelves. There was quite some media coverage, many went to great lengths explaining why EA finally got hold of the Porsche license.
Porsche doesn't sell its license to make money, they manage it to protect first and foremost their intellectual property. They make sure nobody does anything to damage the brand. That's their main interest.
And it's very very hard indeed to believe these delicate matters are put in the hands of a video game company that was
that big back in the days.
To sum it up:
If you disregard the value of the eMail (because it can't be cross-checked), stick to facts about German copyright law (limited possibility of selling original copyright holder's rights) and look at the history of Porsche management (which can be learned by reading the financial pages of any good newspaper) it is highly unlikely that Porsche grants a third party (EA) such influence over managing their brand.
It's far more plausible that (a) PD didn't cough up enough money at all (b) PD didn't cough up enough money to satisfy EA for loosing exclusivity (c) Porsche can't be bothered because PD is just some small Japanese outfit (d) Porsche wants exclusivity and PD doesn't want to drop RUF (e) RUF wants exclusivity and doesn't allow Porsches besides them.
All these reasons are quite probable and sound and follow simple reason and deduction.
They do not rely on any "evidence" that can't be cross-checked.
As I said before, this whole subject qualifies as an urban myth. It depends heavily on hearsay. Everybody knows about this eMail, yet nobody has seen it in person. But knows someone who knows someone who has.
This myth provides an easy (and emotion provoking) explanation. It even has a bit of conspiracy in it. Whereas in reality, it's all about tedious legal matters and boring financial news.
That's about all there is to say on this matter.