Acorn hardware used log encoded samples, while nearly everything else used linear. The simple mod players in games tended not to do any conversion and instead used preconverted mods (which were then a pig to pay in anything else). So it's possible that the Arc mods for Lemmings had been converted from a higher bit rate source, rather than just using copies of the Amiga ones.

Whether an 8-bit log samples sounds better than an 8-bit linear sample when it's not processed through YouTube, I have no idea...