Care to share where you've read about these trojans? I can't say I've seen anything myself but I always like to read about emerging threats.
There's an exploit for ARDagent (Apple Remote Desktop), which can be prevented simply by turning on your Remote Desktop services
These exploits rely on you being a moron and / or having Safari to "open safe files automatically" when downloaded, and even then you'd need to confirm to opening of the downloaded file, THEN you'd have to type in your root password and finally click OK to confirm before it would open / run.
If you're that clueless you shouldn't be using a computer tbh
I'd say it has something to do with the level of competence of the person in control of the vehicle/aircraft.The biggest problem I see is when the first "killer" Mac OS X virus/trojan/etc. hits barely anyone is running software to protect themselves so it'll be able to run rampant.
At least on Windows, you're likely to be running software to stop this happening.
Kinda like flying vs. driving. There are way more things that can go wrong with an airplane than a car, but the fact there's such care taken with aircraft means it's actually a lot safer (statistically).