These differences are perceived as “groove” and therefore people assume it’s all about timing even though this is often not the case. It can be very hard to hear if a certain groove comes from variation in timing, or from accents in terms of loudness or timbre.
I could be wrong, but I think 90% of what people love about the 808 or 909 is how the sound interacts, how you can add accented steps, and how changing levels often not only changes loudness, but introduces subtle timbre changes as well.
None of this is random. It’s partly intentionally designed that way, or it was a happy side-effect of the designers trying to create nice-sounding circuitry with as little parts as possible (this is probably true for how the kick triggering behaves on the 808 ;)).