Yes stammers can be very common in childhood, and disappear on their own.
My dd does it infrequently, and several children i cared for in nursery had stammers that to my knowledge never developed into anything.
My dd has always had large vocab, but as she's getting older (now 3) she seems to like babbling baby rubbish.
I often think that once the novelty has worn off a new development then its not so fun to do, they don't get as much praise, and therefore try some other techniques, or get a bit lazy.
I know your dd isn't babbling, but could there be a similar theory behind it? esp with change - new baby in the house etc.