My mechanic and RWC bloke are one and the same.
He should (and would) fix anything before doing the roadworthy.
I would assume that most people cursed with an annual roadworthy would take the car to the same person who services it, so would expect them to do a pre check before doing the job, now if that precheck happens to be done at the same time as the RWC thats all fine and dandy.
If you just show up as some random and have never seen the mechanic before, thats different, but still, 5 minutes to replace a globe vs the time wasted doing a second inspection (for which they can't charge) seems to me to be more mucking around (for both parties) than a 50 cent globe is worth.