There's definitely something weird going on with the spike hitboxes for D-tilt. Like there's the fact that the angle it launches has been changed and that it has been nerffed from a spike to a meteor, but I actually think that it's easier to land now for some reason. I can only guess that either the spike hitbox priority has been changed or that the hitboxes have been spaced apart to make it easier to avoid the non-spike hitboxes. [It used to be, and probably still is, that you had to hit with the spike hitbox and only the spike hitbox, avoiding all others, otherwise it wouldn't spike.]
I don't have any way of confirming any of the above so don't take it for truth.
Also, D-tilt can still spike people hanging on the ledge. This is confirmed. It's probably just harder due to the spike hitbox being made smaller or something. Try it against Charizard if you want to see it yourself.
Actually, come to think of it, it could be that many of the hitbox sizes on D-tilt have all been made smaller. Someone with both versions please check this scientifically. I only suggest this because it would explain a lot. I could easily be wrong.