I think it all depends on attitude. I am not KJVO, but know some people who are, each with different attitudes about their convictions. In my experience, I have found, believe it or not, a few who more or less stick to the King James (and won't even touch other translations) simply for the sake of "tradition" (for lack of better terms), tending toward more old school convictions, not only on this, but on a variety of other issues. Believe it or not, I do not find such people to be legalistic. It is possible for people to have a conviction on anything while keeping a humble heart and viewing it as nothing more than what it is: a personal conviction. However (yes, a big HOWEVER comes into play), there are many who not only are firmly convicted to read and study only from the King James translation, but view others who disagree in the slightest as no better than heathens! Now this, in my opinion, is legalism... and I know my share of these types, as well.
It's not that I don't understand that people can have honest convictions regarding one thing or another (Bible version choices, what is considered modest clothing, what kinds of music are okay for a Christian to listen to, and so on). We just need to take care that we are trying to stay humble in whatever conviction we may honestly have. This is where Romans 14 comes in. Verse 1 speaks of "doubtful things", then uses eating meat and observing certain days as an example. One who does not eat meat or observe a given day should not condemn the one who does, while those who do should still respect those who do not. And yes, other issues over which convictions and opinions can differ can be applied here. Christians should be able to agree to disagree, despite their differing convictions.
I don't wish to debate, or anything; this is just my two cents.