Unfortunately, that is just not true in every case.

DNS itself is essentially a numbers game but when moving site files, confirming directory permissions or ACL’s, moving email data files, database setup, configuring third party components and many other unknowns, there can potentially be several obstacles that translate into $$$.

This does not take into account the individual or organization that is actually doing the work. If you are the site owner, developer and server admin all rolled into one then maybe you can save a few dollars there doing the work yourself. Speaking from experience, there are very few times when you have all those roles and expertise bundled into one individual.

Most of the site and server owners will end up contracting services that can vary greatly in cost and can without much work at all, exceed a given budget.

I think it is very important to set a truthful expectation to a customer and not one that paints a perfect picture just to seal the deal. This is not to say that not all service migrations or site moves are problematic but the potential for a long weekend is always looming.