The expectation is that Romney isn't going to try to pull a surprise like McCain did last time. He'll leak the names of the top two or three finalists well in advance of making any decision, so that they can be scrutinized in the media before he locks himself into any particular nominee.
That's what it seemed like McCain was doing last time around, when the leaks suggested that it was either Pawlenty or Romney, but then he turned around and picked a name for which the campaign had given no previous indication that they were considering.
That is because McCain panicked, and likes the rush of living on the edge to boot. Mittens is the opposite of that wiring. He never panics, and living on the edge is a poor cost/benefit decision when you get no rush from it. Mittens is facile with penciling stuff.