Your argument is based entirely on RAI. Actually - I agree with you - not counting 'IG' as 'AM' is not clever. For me, if someone was stupid enough to put Pask in one of those variants, I'd go with it.

But you can't just make a leap and 'staple' the IA entries into 102. Just because it doesn't say you can't, doesn't mean you can with 40K. There are no more implied rules to state Pask can go in a Conqueror then there are to state he can ride the back of a captured Defiler.

The tank commander entry specifically refers to a page in the Codex AM that does not have the word 'conqueror' or 'annihilator' written in that entry. Therefore, my comment that it is 'pure RAW' stands.