So your saying because it's less targeted, I shouldn't use it? That's like saying because I have a lower sperm cell count I don't have to use condems.
By your reasoning I shouldn't have to use NIDS HIDS either if I'm running off of a linux server... oh wait most things run on the net off of a unix based system( I'm lumping OSX and Linux together as they are a branch off of unix). But you won't find 1 company that has ANY IT security NOT running these things. Your internet servers... not running windows... still using security... and thier security people would be fired if they weren't as they should be.
Yes, less targeted because lower home user market share... but still targeted and thus still require protection for a smart user. Think of it like this. Soft targets are the targets that get hit. If you don't protect yourself... you stand a higher risk of being exploited. OSX, Linux, Unix, Windows all need 3rd party detection, signature, hueristics, anomoly/behavior based... it's all needed. I know YOUR specifically talking signature based but there are many forms of AV out there ( I just pointed them out). Sorry I'm a security guy by proffession and I think you as a user should be informed.