Perhaps it should, but it doesn't, so if you the player want to be a heavy weapon specialist, you build him like a sniper and give him a big-ass rapid-fire gun. Functionally, the build for both archetypes is about the same (with the exception of a Talent or two, here or there).
It's more than just one or two Talents - those abilities can have a fundamental effect on the efficiency of a character. And that is before we add Weapon Proficiency, which is technically a Talent as well.
But I agree that it would have been nice to have a more granular differentiation between weapon handling reflected in Ballistic Skill Tests as well. A bit like in Shadowrun, where you get a stat for each type of gun, but can optionally default to "related" characteristics.
Oh well, spilt milk and all.