I am one of those professionals. There is a line where it is actually cheaper to buy a new computer than to pay a professional to rebuild the OS, do the updates, re-install the applications, and restore the documents and data on the old one. If that job has to be done anyway, it is often better to take the opportunity to upgrade the computer to gain speed and greater capability.
You know, I wonder how practical it would be to have users save all of their important files--Word documents, Excel spreadsheets, tax-related information, resumes, etc--on a thumb drive or remote server. When it comes time to deal with the inevitable build-up of malware and general system crud, nuking from orbit and reinstalling becomes far more viable, as the user's data is on a separate, uninfected drive.
This is true. But, on the other hand, if you say to someone, for an hours worth of work, and you charge $70 minimum charge to work on their PC, most people will pay that to get back to where they were before they were infested, rather than have a whole new Windows install with all that goes along with that.
Amen to that.
I have a number of folks that I do such admin work for and I find they are more than willing to spend the money (hell...they've GOT it) on a new machine when the old one takes a voltage spike, gets slogged with malware and crud or whatever.
They are even happier when I tell them I'll set up their old HDD as a slave backup unit. I then do snapshots as backups for them on a regular basis (Logmein is a godsend) and all their stuff is safe and recoverable.