The magic of statistics was not that they were per-step, but that they could be combined over multiple steps with `getSummaryStatistic`.  They were never documented, and in fact `getSummaryStatistic` was never even used within the Buildbot codebase.  At any rate, they're easy enough to emulate with properties -- either by tagging with the step name as Pierre has suggested (if that's what you want), or by using member variables, or by doing the summing during the execution (as I've done with all of the existing uses of statistics).  All of which is me trying to convince myself that they should be removed.

But you're right - the effort to keep them is minimal.