Are all BB shells intended for road cranks close enough in width that one length of crank spindle is all that's needed? Which I guess means the reach of the crank fixing bolt is enough to make up for the difference in shell widths?

I ask because I want to switch from a standard crank to a compact along with going from a cartridge BB to a BB30. And looking at the options available at the online store's website, there is no option to select a specific spindle length, and for some reason that seems odd to me, so I wanted to check.