In terms of the average person, replacing parts isn't really part of the equation - you realize that 90% of the population is afraid to replace their RAM let alone a mobo, video card, RAID cards, etc.? I agree that PCs in terms of expandability and flexibility can't be beat. However, for a good majority of the computer buying public, they just want to buy something that they can use and not have to worry about. I think that's something that people like us who are comfortable with technology and know it inside-out tend to lose sight of - the average person and their usage patterns. The computer is fast becoming an appliance - your average Joe Shmoe wants to just buy the thing, put it in his office and not have to worry about it. As for me, I went with Apple because I was tired of playing repairman with my 98/2000/XP machines, I just wanted to get work done and let the tech slip into the background.
As for laptops - that's the risk you take. I need something portable for field work. Necessity trumps any kind of perceived risk. And my return on investment for a laptop is tremendous - I now use my MacBook Pro more than I do my desktop system. If I continue using it the way I am for the next 2 or 3 years with the kind of jobs that I'm doing, the productivity (not to mention flexibility - I can lug a 5 pound laptop around with me to photoshoots and other studios, while with my PowerMac I need to wait until I get back into the studio until I can do anything) that it allows more than outweighs the $2000 that I spent on it.
So I guess you could say that Macs are the easy way out. But after working on/with/against Windows systems for so many years, I'm fine with easy.