one other point i should make, is a lot of the extreme prevention I take is due to the fact that I have a 450g with a lot of fish. i simply don't have the option of failure. were there situations I felt near 100% confident I could skip QT? Yes. I have even taken fish from people that I know had Ich-free tanks and still QT'ed the fish. The day Ich sneaks into my tank, I have no clue how I am going to house this many fish while running my DT fallow for 3 months... and then to TTM all of the fish, forget about it.
if you have a small enough tank (< 150g, IMO), then the ramification of Ich-failure is not that bad, just time consuming... assuming you don't lose fish over it, which isn't fair to the fish, but quick acting will fix that.
that said, as I mentioned, it is a gamble if you don't QT any specimens, anything wet. educated and non-impulsive decisions are where you are going to be on the winning side of the gamble. and at least you are asking questions now and will know how to react in case something goes wrong.
just remember, Vegas isn't paved in gold due to their shows and cheap buffets!