The point is that Bulbasaur starts out as being able to stand on its hind legs if it wanted to, then Ivysaur loses that ability due to the bulb on its back growing bigger, and by the time it's evolved into Venusaur, it's a pokémon with a giant flower (rafflesia, iirc) on its back, and the pokédex shows that its average weight increases by ten times between evolutions.
