With the field split as many ways as it is, as early as it is, that's still very significant. Gingrich and McCain have absolutely no chance, so their numbers will have to go somewhere. If Rudy only pulls 1/3 of each withdrawn candidates' numbers, he'll be able to carry the day easily.
At this point in 2000 the field was split as many ways as it is now and Bush had significantly higher levels of support. In may of 1999 Bush broke 50% and by August the race was over with Bush polling in the mid-60s.
Rudy supporters are working hard to create an atmosphere of inevitability, but with a huge chunk of voters still unaligned it shows we have a long way to go.