So the sentiment that crappy computers are good enough for casual users is exactly backwards: casual users are the ones that need high-end computers, while proficient users are the ones who can work around the limitations of crappy computers.
A great argument that the casual user's claim of "I don't user computers for much so I'm going to buy the cheapest one available." becomes a self-fulfilling prophecy. My only disagreement is that power users shouldn't use a crappy computer either. Everyone should have fast computers and retina tablets.