Maybe i am reading the manual wrong.
On page 18 it states that:
A damage 3 weapon is required to kill a Abomination. To slay the the monster, you need either a trebuchet (page 24) or to throw Dragon Bile and ignite with a torch.
So you can kill a Abomination with the trebuchet.
Or am i missing something ???
Yes. You're missing the rules of the Abominatroll (or perhaps the wording of the OP's question). It's a special abomination which can only be killed with dragon fire.