Opssys
It really isn't about any analysis as such and I don't know of any 'standard' of 25 minutes for the 737- it's a target; and at the most basic level it is simply about optimial aircraft utilisation.
The 25 minute turnaround on the B737 is achieveable most of the time at some airports, but not achievable all of the time at all airports. Smart airlines know that and schedule accordingly taking into account historial turnaround data at a given airport. What you don't see at the turnaround is the scheduled block time for a given sector which will often soak-up some of turnaround delays and provide the ops controllers with a bit of schedule recovery. But the point you make is valid- with unrealistic scheduling you can carry a morning delay to late in the evening if the line of flying has no buffers or you don't have an opportunity to swap the delay out by using another aircraft.