Yes. Although, for Greyhawk, it's a lot easier to ignore stuff that isn't being created. Mind you, I ignored the Greyhawk Wars as well (or at least, used a version that is quite different to what was printed).
IMC, Vecna replaced Iuz due to the players mucking up "Vecna Lives!" That then changed the emphasis of the Blades of Corusk series by having Iuz trying to regain a powerbase. Lots of fun.
The PCs managed to _not_ stop the Fane of Scales (see a recent Dungeon Magazine) when it fell in the Great Kingdom, nor did they stop Daglan (of Feast of Goblyns) from taking over part of the Great Kingdom, so that's caused the GK to be very nasty indeed.
Ulek is currently in an Ice Age due to the incursion of the Fhoi Myore - I rather hope the PCs are able to stop them!
Fortunately, the Champion's Games passed successfully for the forces of weal, so I don't have a large undead uprising in the Free City.