Wow, you guys would really hate the level 20 Spellstorm power, teleport all enemies in a burst 10 to anywhere within the burst 10, int v fort.
What possible justification can be given for changing the way a power works, except for a DM just not wanting to deal with it? This comes down to DM responsibility - if a session is going to take place over a 1,000 foot drop, there should be a reasonable expectation that someone, a PC or a monster, might fall off that drop.
So let's nerf bullrush, so that PCs can't push monsters over the edge. Let's edit Tide of Iron, so that shield bashes mysteriously are incapable of moving monsters off the sides of edges. Let's edit teleport, so the ability to move anywhere is inexplicably now confined to surfaces that could be stood on.
This is unreasonable. The power does what the power says it does. The DM shouldn't be in the business of changing PC powers just because he's not clever or thoughtful enough to take those powers into account ahead of time. Let's just decide that radiant damage doesn't do extra damage to undead, to prevent multiple divine party members having too easy of a time, while we're at it.
If the DM is so foolish as to not expect someone to fall off the 1,000 foot drop HE installed in the combat area, he shouldn't be in the business of DMing.