Comment by necovek
Uhm, this still sounds like just bad math.
While it's non-obvious this is the effect, anyone analyzing the results should be aware of it and should only compare weighted averages, or per distinct time periods.
And therein is the largest problem with A/B testing: it's mostly done by people not understanding the math subtleties, thus they will misinterpret results in either direction.
Agreed, and articles like this don't help. That's the only point I was trying to make really.