A couple of things:
Being the favorite son in one of the early states is not the advantage you might think it is. Basically, the result gets downplayed completely.
And, let me assure you, Senator Sununu would not fare well in the Iowa Caucus'.
Could be, but he lives there, he can campaign till the cows come him till the day of the primaries and skew the field.
On the minimum, its an intimidation factor.
Now Iowa is a different story, Sununu would have problems there, but in essence, its the only one he would really have to work, if you take the first 2 states, the odds are very very good, that you'll be able to ride.
Either way, this is all moot, I honestly don't think Sununu has any interest, at this time, what so ever, in running in 2008 for prez.