Yeah, I can appreciate why people don't switch when there's something they need to be able to do (eg. Quicken or online classes) that they couldn't with the new software.
But it seems to me that some people are just resistant to change and won't go to something new unless there's a compelling positive reason, ie. to do something new, and a negative reason (avoiding malware) won't suffice.
This is exactly it. I am certainly technical enough to run Linux (and have in the past) but there's no real good compelling reason for me to use it. I don't get malware on Windows and, believe it or not, things hardly ever crash. And you know what? I actually like using Windows. I can run basically whatever I want and use basically any hardware I want. I'd rather get work or play done on my machine instead of tinkering with every little config file and stupid little problems that always occur in Linux. Win7's UI is fantastic as well.
The other problem is that she takes online classes and they tend to use packages that have very fussy browser support. I wouldn't trust that it would work on Linux without a thorough test -- don't want to find out you have a problem during a timed test.
Mac was rejected on cost (she went with a sub $600 laptop).