Nah, Roy's was called Flare Blade, not Eruption. Visually and conceptually they are similar, except Roy's is generally a 1 Hit-K.O.
You were being serious, right?
...It functions nearly the same as Flare Blade.
If it wasn't an original move, that's the only move it could've been based upon. Making similar moves isn't odd. Fox and R.O.B.'s Laser, for instance. They're both lasers, but have reasonable differences. Or should I note how similar Fox and Falco's are, the only difference being damage and knockback.
He makes similar moves from time to time. It honestly does feel like Ike is a re-vamped Roy, not that that is the actual case(not that it wouldn't make sense, but we have no idea what went through Sakurai's mind. He hasn't talked about Ike's creation in Brawl, unless I missed something...). He was separated from Marth, suddenly has Fire abilities... of course, it's probably just a coincidence. Or even just a one-move thing and nothing more.
We have no idea how Roy would've been if he made it in. If Toon Link is any indication, he could've still been a clone.(albeit, while I know Toon Link being a clone is because of Sakurai saying it was a "rule" to have him and Link have the same B moves. What I mean is that Sakurai didn't leave clones out. Giga Bowser is another playable one. Alloys are also A-Move clones of the originals. He moved away from clones a bit in Brawl, but at that point in time SSB-wise, clones were normal. We have no idea what For will hold, though. I'm hoping for none beyond the Fighting Team at best)