Whatever works, but that difference may simply be a scanner or scanning software thing, not an issue with the negative.
I thought the same thing, but I've scanned HP5+ shot at ISO 400 and the shots always seemed underexposed or were boring and didn't really work for me. For the actual first time, I actually like the shots I took. (I'm still learning).
But then again, I could come up with a cop out excuse its because of the lenses I'm using for this shoot