Sarisio: WoW wasn't a sequel to anything though, it was stand-alone game, having connection to Warcraft RST series just in name.
However, if people imply Cataclysm, I full-heartedly agree. But I guess such is the fate of any MMO - change of directors/game designers -> completely ridiculous expansions. Not really much for persistent world...
ZFR: It continued the storyline; and in my opinion completely destroyed it.
Should there be a Warcraft 4, its story will have to take into account WoW and other Warcraft games. It won't be just a continuation of Warcraft 3.
Actually, there are ways around that issue. For example:
Zelda: Ocarina of Time introduced a timeline split. As a result, Zelda: the Wind Waker could be made despite its plot contradicting those of earlier games.
A sequel to Chrono Trigger need not take into account Chrono Cross; it can just say Chrono Cross took place in another dimension. The additions to the DS version of Chrono Trigger do not contradict that; to see the connection, you need to go through a dungeon called the Dimensional Vortex, which can be interpreted as taking you to a different dimension.
One interesting case is in the Elder Scrolls. Daggerfall had multiple endings depending on who you give the artifact to. When its sequel came along, the developers, instead of making one ending canon, introduced a "Dragon Break"; all the endings occurred simultaneously.