In all fairness - the relevance is towards realism. I know it's a game. I know it's sci-fi, but still it is not Transformers or pokemon.
Obliterators in 40k can morph into: lascannon, multi-melta, plasma cannon, twin-linked plasma gun, twin-linked melta gun, twin-linked flamer. I cannot find any other specified weapons in the fluff and no AA-type weapons whatsoever.
Lascannons can be AA, however they are never counted as such in Infantry units. If Oblits should have AA why not give AA to any other lascannon wielding infantry? Why not? they have an 'energy weapon' so you just point it at a flying airplane, go 'bzzzzz' and it should blow up. In case someone mentions 'Obliterators morphing targetting systems' - please give me an actual quote and by Perturabo, I will shut my yapper ÂÂ

Instead of making obliterators fluffy , they seem to be AA oriented which has no proof in the fluff. We're trying to make Obliterators omnipotent. They can't morph into a battlecannon, but somehow they can morph in to AA designated weapons. IMO this doesn't add up.
a quote in the rulebook (pg 48) concerning aerospace units:
Quote:
This sheer speed means that only specialised ground units and other aerospace units are capable of engaging them.
I cannot find any proof of oblits being specialised in AA or have any AA abilities and the quotation above should remind us what we are dealing with here. ÂÂ
Laylo