This isn't meant to be a serious statistical analysis, just an observation.
Seems to me, one of the problems that plagued the Rams in the red zone over the years was Steven Jackson's inability to score a touchdown, especially when it counted. I seem to remember a stat from STL Today around when SJ39 left, mentioning that Steven Jackson tied or beat Marshall Faulk in the franchise rushing TD standings - and yet, it took Jackson about twice as much time to do so. Let's face it, he was good at pounding out yards and getting us down the field, but after that, his key red zone strength was in setting up the play action and pass protection.
The way I see it, Stacy gives us that and more (disclaimer: with the limited sample size we have so far). Three rushing TDs in the six weeks since becoming the starter puts him on track for three more before the season ends, and a theoretical 9-10 for a full season - and if his recent consistency finding the end zone shows anything, it's that his lack of success the first four weeks were just him getting used to the NFL, not a lack of talent. That easily beats SJ39's pace for the last five years straight.
Maybe he's running behind a better offensive line, and has better receiving talent, but the argument can be made that losing Bradford nullified those advantages. The best thing I can say is, Stacy looks like a better runner using his small Ray-Rice-like size in crashing through holes and scoring, and scoring is ultimately a better way to keep defenses honest than just threatening to.