Zeus is not compatible with Linux, and most malware isn't either, because Windows is fail and idiots use Windows (double fail)
Most malware isn't compatible with linux because the vast majority of users use windows. Creating a botnet with linux bots isn't harder than targeting windows machines but the turn over won't be as great. Also most desktop linux users are poor communists so it's not worth stealing their financial details.
Exactly correct, the reason there isn't much malware development for osx or linux is because the market share just isn't large enough to make it profitable. I know because I do virus removals for my living. Average day I get ~10 pcs 2 macs... about once every 2 months I get a linux user who I get to laugh at and say "just nuke the box".
But I do have to say this, the vast majority of infections are detected by AV like norton, trend or kapersky. All of the potentially useful malware is well defined and nearly impossible to hide. Most of my business comes from people who were informed by AV that a virus was found and removed. Then it's a 20 or 30 min thing for me to remove the source (whatever trojan/dropper/rootkit) they've actually got. And that's if I have to manually track it down and kill it use AR/PE/HJT. in the vast majority of cases TK and MBAM catch everything.
Additionally, most AVs now monitor performance, and would alert the user if resources had high usage. Heck it took the AV community (and virus removal techs specifically) all of 2 days to identify Zero.Access, a week later it was defined, and a week after that we had a reliable removal process pushed out to every av source that matters.
TimeTillDeath on your average botnet (remote administration tool) is a few days or weeks at best. Assuming the user had an AV installed first.