I'm wondering if the Wii fixed the disc errors that the Gamecube had, they probably did but want to make sure.

I have experienced a couple of errors on my Gamecube:

the GameCube has failed to read the disc (something along the lines of that)

and "an error has occured, please turn off your system and check the manual.. etc"

Oh ok, so I guess it is the both the disc and system's problem with my Cube.
The 2nd error I stated only happens with one game.
The 1st error happens with one game.
Well they are both Super Mario Sunshine, but different copies.

The 1st error happens to a FLAWLESS DISC - no scratches AT ALL.
I don't get it.

The 2nd error happens on a badly used disc.

It's never happened to me with GC discs either on my Wii or on the Gamecube.

Same.

Never had an error at all.

My cube however used to freeze up sometimes on Metroid Prime when I was on a lift.  But never when playing it on Wii.

That's good to hear, I'll eventually be hooked up with a Wii again, the Gamecube is just a temporary used set up to hold me back until then.

That happens every once in a while with my Gamecube. I just take out the disk and put it back in again with no problems.

that happens to me alot with my wii, maybe it has something to do with my GC games being full of scratches and dirt.

I had 1 GC outright fail, but out of the 3 I owned (2 with family, 1 after moving out) only that once console gave us any problems at all. My Wii has never had a problem reading GC discs.