So getting away from the power weapon thing for a sec:
The language on grenades and difficult terrain and initiative 1 used to be something like "if the unit takes a difficult terrain test, it attacks at initiative 1 (unless grenades)"
Now the language has changed to "if the unit moves through difficult terrain"
Now various units, such as Wraiths and Beasts (now) ignore difficult terrain. Jumpers, it seems like, can actually jump over terrain, if they didn't use their jump packs in the movement phase.
In the wraiths case, it says "Wraiths are never slowed by difficult terrain"
Previously, that would have meant they don't need grenades. But now, they're still passing though the terrain......wouldn't that make them Initiative 1? (not always a big difference, for them)