(((HUGS))) Debbie ... I can certainly understand your concern, afterall you are Tubby's meowmmy ... and that's what we meowmmies do best! Like you said, it's great that he isn't losing weight, and I think the vet is just trying to give him the best of care, so as to be sure to catch any changes asap!
Give that big guy a kissie from me please! Oh, and pictures, even sleepyhead ones would be GREAT!

Kim