I just read in the December issue of EDGE that rather than Emulate the original Fantasy Zone for Fantasy Zone Collection on PS2, they actually re-made the ENTIRE game from scratch, including re-drawing and re-animating EVERY FRAME of animation and re-writing the entire game to be just how it was in the Arcades!
Totally pointless! But cool none the less B-)
Did they give a reason for that? I mean, they just emulated for the Saturn Sega Ages version, didn’t they? And I assume they didn’t just feel like not repeating themselves?
I dunno, most of the games on Sega Ages for Saturn are ported rather than emulated - OutRun etc.
They may have specified a reason, but it wasn’t really gone into in much depth in Edge other than the fact it was actually done. 
My guess is, it may have been done to add extra features, you could add extra touches if you had a source code to work with.
Although I don’t really understand the whole re-drawing and re-animating every sprite thing… you could just rip them straight from the Arcade roms and be done with it :-/
I think it may have something to do with the much higher screen resolution that we enjoy in this HD era. The intensity of detail means that many original sprites now appear extremely blocky, crude and ugly - redrawing them is necessary for smoother images and animation. Megaman 9 does a similar thing, using filter effects to smooth out the ragged edges of its retro graphics.
They didn’t change them though… they just re-drew them exactly as they were in the Arcade version :-/