One more - if the fiddle is extended in front of you how can you see properly to tell where you should place your fingers in order to be spot on tune ? Guess a lot ? At least on the mandolin you can see the fretboard when you play.
You can still see your fingers, you're just looking at the fingerboard end-on instead of from the side/top. Stewart's right that listening to the notes lets you "fine-tune" your pitch if you missed slightly, although this is looked down on by classical musicians. ;-) Perfect pitch isn't needed, but relative pitch certainly is. Most people have it, but a few haven't. Unfortunately a guy in our club doesn't, and he's been learning fiddle for the last 4 years or so. It's a shame cos he's a not-bad mandolin player, but he hasn't got the ear to play fiddle.