I think Jazz's size falls victim to the cost spread that the designers are trying out with this line - ie: some toys within your Deluxe Price Point are more expensive to produce than your typical deluxe, whereas some are less and the balance is spread across the line to come out even.

The other example of this is the Wave 1 Optimus & Starscream - Optimus being a smaller Voyager and Starscream being a slightly larger mould.