Is there any actual difference between these, other than BB giving a bonus to Hoist?

You cannot get bulging biceps with minions due to high requierments (unless you give them skeletal petrification).

That's it? I thought there might be some subtle difference between "always counts as braced" and "doesn't have to brace."

No. In former times, Autostabilized was a lot better because it made Full and Semi Auto into half actions, but by BC, they're half actions anyway.

I'm not sure that I'm totally happy about even a Space Marine being able to move and fire a heavy bolter as if it were a rifle.

umm this is an argument of talent vs weapon augment?

There simply seems to be no difference between them,

think of it this way:

Bulging biceps costs x amount of xp, but after that you're good to go with every heavy weapon as you like.

Autostabilized weapon trait is received via upgrades, which are easy to come by eventually, but is only suitable to the weapon you?re looking to add it for.