In patch 4.4, Kassadin was listed as being reworked because many of his abilities had been changed. However, there were a lot of changes to Maokai in patch 4.11 but he wasn't listed as being reworked. What distinguishes reworks from general buffs/nerfs?
Kassadin counted as a rework because a few things were fundamental changed; the same was not true for Maokai.
Kassadin lost a Silence and gained a shield. He also gained an auto-attack reset to smooth out the damage curve. There were changes to his numbers and ults but the main point was, you can now fight back and Kassadin needs to melee you for full damage output.
With Maokai, the primary change was the ultimate. While it does change his play pattern, much of the general pattern from before remains the same unlike Kassadin. Maokai has always wanted to toss saplings, he's always wanted to stay close to allies or W > Q initiate.
Makes sense?
Scale of changes.
A gameplay update often changes numbers, and slightly changes abilities. A rework often scraps much of a champions kit, to create better gameplay and to make sure the kit fulfills the champion archetype
