Yes, it is an ego thing, and exaggerated for rhetorical effect. But no more so than the attitude of so called "customers" who think they deserve respect simply because they have money in their pocket - which, by the way, they resent having to spend. It's a two way street.
It occurs to me that if a person who can fully assemble a bike by himself wants to use the services of a bike shop to cut his steerer tube, he must be after an extra special expert hack job, not just an ordinary one. So of course there would be a premium to be paid
Of course if he'd gotten his own bike building skills from being friendly with the mechanics at the shop, they might have done it for him free of charge.