Many guitars made now have a steel reinforced neck (with the exception of traditional classical guitars which don't need one as the string tension from nylon strings is not sufficient to require it) but a steel reinforced neck is not necessarily an adjustable truss rod.

I was given a small semi-hollow bodied electric guitar with a neck that was terribly warped. It was twisted and bowed way beyond anything close playability. It was twisted so severely that the headstock was about 30 degrees offset from the heel of the neck. I removed the neck, bolted the heel to one small plank and the headstock to another. Using clamps on the workbench and planks to apply twisting pressure opposite of the twist and heat from a hairdryer I was able to straighten it to near perfect in a couple of days. Heat it up, increase the clamp pressures, let it cool and repeat until the neck was straight and it played really well once re-assembled.