Dire Bare
Legend
Absolutely. You've got non-optional wacky PC races coming out every year that you're supposed to adapt your world to, of course it's hostile to worldbuilders. Yes, you can ban things, you can also add things to fix the system, but that doesn't get around that as written, the game is a step backwards for worldbuilding purposes.
I have a hard time seeing anything in 4e (or any version of D&D) "hostile" to world-building. It's guarunteed that at some point or other, some official "piece" of D&D lore is published that you won't like. Easy fix is not to use it. Or to change it to suit your tastes.
It goes back to an open GM style which encourages the DM to say "yes" and a closed GM style which encourages the DM to limit player choices.
Right now, in my home campaign, I don't have any plant races. And I'm not going to worry about it much until either, A) inspiration strikes and a plant-race like the Wilden suddenly find a reason to exist in my campaign, or B) a player asks to play a Wilden.
When I'm confronted with "B" above, I could get all angsty and shout, "NO! Silly plant people just don't belong in MY world." Or I could be open, say yes, and work the Wilden PC into my world. Wilden don't have to become major players in my campaign (or they could), all I need to do is be creative and find a reason why this one Wilden exists in my campaign. I can use the fluff from PHB3 unchanged, I can alter it, or I can throw it out altogether and come up with my own.
"Hostile" to world-building? No, it is a creative opportunity to expand my world.