I want to play devil's advocate here. From the management's side, they don't want to spend more, because if they figure the client would most likely buy a new racket, instead of trying to repair the racket. If you don't tube a bad grommet, that will most likely lead to string breakage. That's more percieved dollars in the company's pocket.
Though I agree with all of you, that it's the stringer's job to replace head guards/grommets, tubing, Grips and string. That's pretty much the job of a stringer. Anyone who does not do want to do that should not call themselves a Stringer.
BTW, I've seen my fill of abused "Junior" rackets, even adult rackets.
Machines: Gamma 6004 2-point w/ Wise 2086 & Babolat Sensor Dual