It's pretty clear they want to avoid or limit the ability to use forced movement to get free damage. Otherwise OAs would still be provoked.I don't believe they are, or it would have been mentioned in the PHB under the forced movement section, or the powers section under Zones. Or somewherein the PHB, if that rule was intended to be used for player powers.
In my opinion, that section of the DMG is for terrain hazards, not effects created by powers.