I think coromonadalix got confused.
IDE has always had 40 "signal" wires, but ATA/ATAPI/IDE/whatever standard will only work faster than 33MHz with 80 wires.
As you said, the 80 wires improve the signal integrity, reducing crosstalk/coupling (shielding) by interleaving signal/gnd/signal/gnd... thus allowing faster signals.
Check ATAPI-4 (Max 33MHz) and ATAPI-5 (Which introduced 66MHz and 80 wires), later standards improved up to 133MHz (edit: It seems they also made a rare 166MHz version, never saw it anywhere), but all using 80 wires.
Still, it was pretty common to use 40 wires for CD/DVD drives, 80 wires weren't required as their speeds wouldn't saturate a 33MHz bus, and the cables were cheaper. Fastest DVD: 16x * 1385KB = ~22MB/s