Linux is no different than Windows
That, to begin with, is utterly wrong. The big difference between Linux and Windows is that it's open source. (Remember: bitcoin is opensource too, and if it wasn't, it wouldn't have been so successful.)
people should really stop thinking that there is something magical about it
I've never brought up magic in the conversation. I tried to explain why opensource software is more secure, in technical terms.
You don't need to install software as root to infect your machine with malware. Obviously, if you do it the malware has full access to the machine but running a trojan with your own credentials is enough to steal your wallet data.
I never brought up the subject about root vs non-root permissions (which BTW it is something that is better designed in Linux, compared to Windows), but about the way that users install software. Remember, you can only be infected by installing software (documents cannot infect viruses, except for rare occasions in which the document contains executable macros). And you have to analyze how people typically install software in Linux, versus how they do it in other operating systems.