I think that's actually a codex by codex RAW issue. In general though, you don't really care if your terminators have access to the armory, since it's pretty restrictive to what you can give something in terminator armor. You can already give them all the power weapons you could imagine and get the option of cooler weapons like assault cannons. In general though, I think if you buy "terminator honors" you are buying access to the armory, but if you but a terminator squad, even though they sort of have terminator honors included in their profile, you didn't specifically buy it and then don't get to buy armory options.