Actually I'm not all that interested in the safety of the host system so much as the removable media to be honest. Host systems are connected to the internet for home users, which means that one day, some way, you are nearly garaunteed to catch something you don't want. However, removable media can be protected from the insecurities of being connected to the web, by simply not being connected to it. If one were to, say, regularly reinstall their OS using a 'pure' removable device often enough, worms, malware, spyware, most low level rootkits, all get wiped away. I would prefer the absolute assurance that every scrap of data ever transferred onto removable media is approved by a user. Not some algorithm. In truth, one could do such a thing with an isolated network as well, so the same could be said in extension to systems which are designed to never receive internet traffic but transfer sensitive data between a private network which is only connected when a user physically connects them.
Don't get me wrong, networking security is important, however to me the cold hard fact is that every single moment that we connect our devices into a global network, we are exposing that equipment to an environment which will never be secure. No matter how far into encryption we get, how deep security protocols run, how lovely the software... there will always be someone that can and will prove to the world they aren't safe.