do stock rockers ever need to be adjusted?

 

Not unless they're making noise or you have reason to suspect they're misadjusted. Locknuts have been known to loosen up before but that's not very common on an engine that has thousands of miles on it w/ no valvetrain work.

 

As an engine wears, adjustment will change slightly. Modern hydraulic lifters are mostly meant to be left alone. That's why the stock preload has such a wide variance. They can run at anything from a full turn to almost none and still function ok. Most motorheads are going to check them every once in a while.