I have a hard time believing that garbage men and janitors would describe their jobs as useless. They may be undesirable (to some) but there is no argument whatsoever to be made for them being useless.
It may just be the common perceptions of these jobs are so pervasive, it influences the worker's own assessment. It's certainly in character for the bureaucrats to consider their jobs to be important. Desensitized to petty politics and constant surveillance, they probably thought their answers would get back to their boss, and didn't want to appear redundant.
