I see your point actually. IIRC, 0.18 added planets, 0.19 added wheels, kerbal expressions, re-entry effects, removed the launch tower, remodelled the runway. 0.20 added seats, a wheel, and flags. 0.21 was pretty good, with new buildings, revert/removed end flight, changed SAS. 0.22 added science (not much of it). 0.23 added an engine, tweakables, and a bit more science. It's not that consistent.