Abraxas said:
I believe the question comes up because EBT doesn't follow the procedures for grappling - there is no touch attack to initiate the grapple.
That is one difference.
Abraxas said:
The spell uses an opposed grapple check instead of a saving throw to determine if creatures within its spread are affected.
This is a difference between EBT and other spells, not between EBT and grappling.
Abraxas said:
Also, damage for an unarmed strike from a large creature is usually 1d4 not 1d6. (note: Like unarmed strikes, tentacle damage is bludgeoning damage)
A second difference.
Abraxas said:
Separate from that, do spells have to explicitly state they do non-lethal damage for the damage not to be normal?
In this case, the spell explicitly states that the creatures are grappling. Hence, the grapple rules are used unless otherwise specified.
Once the tentacles grapple an opponent, they may make a grapple check each round on your turn to deal 1d6+4 points of bludgeoning damage.
Abraxas said:
And a question, assuming the spell works the way you state, do you give the tentacles iterative grapple attempts based on the high BAB?
Again, using the quote above, it indicates only one check (the word check is singular). This is a third change from the normal grapple check rules.
Just because there are differences does not mean that you throw out all of the grappling rules. You just throw out ones which the spell indicates are different.
Now, an argument could be made that Bludgeoning damage is not Nonlethal Bludgeoning damage. However, unlike the other three differences that you have indicated, bludgeoning damage is not a change from the normal grappling rules since the normal grappling rules do bludgeoning damage. So, this is not an explicit difference, unlike the other three you quoted.
Basically, it comes down to "spells are lethal damage unless indicated otherwise" versus "grapples are nonlethal damage unless indicated otherwise". The reason the grapple rules trumps is because the spell is indicated otherwise, it is indicated as a grapple.
The spell is extremely potent and deadly for a fourth level spell with the damage being lethal damage. Given this, it seems logical to interpret based on the normal grapple rules as opposed to some new rule (EBT does lethal damage, even though grappling does not and even though the spell does not actually state that) that is not explicitly indicated.
If grapples did stun damage as well, so would the spell. For the spell to change something in the normal grapple rules, it does have to explicitly state it.