"Modern aircraft require less maintenance than older aircraft."
I think it would be better phrased as "our regulator require's less maintenance on aircraft".
Each old aircraft bears similarities with their replacements in regards to maintenance requirements in a line environment. IE; the 380 vs 747-400, and the 330 vs 767, and their reliability/maint demand. You could probably argue successfully that the newer types do drain more manhours during turnarounds.
What has changed though, is the maintenance procedures and certification privileges required to keep these aircraft operating in this day and age. The requirements seem to have become less stringent IMHO.