Why are they polling registered voters instead of likely voters?
A gold star for you - that is the key question. Newt's voters are a lot more excited than Romney's tepid supporters. Even those who don't love Newt hate Romney so much that they will be there. To be fair to CNN, they normally go with registered voters, so this wasn't a particularly pro-Romney decision (and to be honest they do that because registered voters are always more liberal than likely voters, so this was a pro-liberalism decision).
It’s 369 likely Republican primary voters.
Small sample size, particularly for a state like FL, so that puts the #s in question.
Still, Newt is having a bad day it seems, so the threat is very real here.