A 'hidden cost' of being a pro Locked

This is not accurate. I have added memory and swapped out HDs on every Mac from a mini up to a Mac Pro. One cannot change the video card in anything less than MacPro but for most people that is not really  a concern. Moreover the myth of upgrading is belied by the fact that most people never do anything other than add memory or change the HD.

The fact that PCs can be "upgraded" is a questionable virtue as the time and expense involved in changing the processor on some old motherboard leaves you with a "faster" machine with all the same old slow support for the rest of the machine.  Even then my PC friends spend hours tracking down drivers and trying to resolve device conflicts. Kind of like putting an expensive engine into a ten year old car when a two year old Honda is better from the get go.

As to the migration of data, my opinion is that a photographer that makes  a living from their work should have all client work on separate, redundant attached drives . New computer? No problem. Connect to your data via the network. Redundant drives allow you to take on off site each day for greater security.

The more stuff you have one the drives in the main machine makes you less flexible.