Narsil and TGaT are NOT the same, for the same reason that has been mentioned by several people in this thread. Perhaps I can explain it differently.
All examples that you are using that "prevent" wounds are RESPONSE actions, meaning the card is already in play, the action has already been paid for, and the results are about to be carried out. The RESPONSE action then prevents the wound from happening.
The card TGaT (and the others like it from RoTEL) actually allows itself to be prevented, NOT through a RESPONSE action, but as it is being played. This distinction is very important, because it means the EVENT is prevented, and the effects never happen. You are not preventing the wounds from TGaT but you are preventing the event itself from carrying out. I know this sounds like splitting hairs. SgtDraino has assumed that the words "to prevent this" on TGaT refers to the act of wounding, but many people have pointed out that it refers to the resolving of the card, which if the FP player does not discard two Gandalf cards, will THEN result in two wounds, to which the FP player could use a RESPONSE action to try to prevent (and fail when at Steward's Tomb).
The fact that the FP is not responding to the event is the key here, because it means the event is still being played and we have not yet come to actually resolve the effect of the event (i.e. the wounding). In all the examples being given where a FP card "cancels" something, it is actually already in play, because the FP is RESPONDING to the event/action/etc. TGaT hasn't come into play when you are "preventing" it from coming into play. (You can't cancel something that hasn't been played).
This explanation is fine, but from a strict rules standpoint it's more personal interpretation, which is a little different for everyone.
The full basis for the argument
for it being able to work at the tomb is merely "Events have a Pay X to do Y format" and "The way the card (and all such cards) should have been worded is "Spot X to make the free people's player choose: A OR B.""
It's more speculation to say that "this" refers to resolving the card as opposed to "preventing" the wounds.
Also there's a bit of a contradiction between your reasoning (which seems sound) compared to my above quotes from Merrick. If the event is "Pay X to do Y" then you have "Spot a Nazgul - Pay X, to wound Gandalf - Do Y. According to this the requirements have been paid and the card has been played.
You could further argue (though there is no actual basis in the rules for it) that "preventing" the wounds is resolving the card, but
it still wouldn't matter if you were, as wounds can't be "prevented" at the tomb.
I think that the big issue is getting lost in the details:
Whether or not you are "resolving a card" it you are still "preventing" wounds as stated on the card, which isn't allowed at the tomb. To say that something "should have been worded" that way (as above) in order to try to fit a tough situation into a mold that we have created, is just more twisting and speculation.
I wouldn't call myself an expert at all, I know there's players like Merrick and Bib who have played far more (and played other games as well) who has more experience....but it's just my opinion that the situation is clearer than we're making it. There's no
specific ruling, as it applies to this context, about whether event wounding can be "prevented" and game text wounding/burden addition (like
morgul brute) can't. So why try to redefine what prevent means here? It says they can't be prevented. The card says you can do something to prevent them, just like
Morgul Brute, which you could do at any other site. But you are at the tomb. They can't be prevented.
If we're actually supposed to just do what the card say (which is what I learned is the golden rule of CCGs from people here
) then let's just do what it says.