I don't know what drum machines UW use exactly, but I do know for sure that their drum machine shows that behavior.
Here is a closeup on a kick of Crocodile. You can see how the waveform suddenly drops down and up again. Both Rowla and Confusion have
very prominent kicks, thats why I used them in the comparison. And it's surely no DC offset because the waveform is perfectly centered. The pic of the waveform is a bit misleading.
Here is a better one.
May I ask what CD your waveform is from?
I've just checked, and all my copies of STITI have that.