Might be kind've hard to say if they were "better" in, say, 1973? That's 33 years ago, so, even if you had an old one and compared it to a new one, the old one is "old" - hard to say if IT still sounds like it did so many years ago??? Components, no matter how good, do age. I surely heard them 30 years ago, but unless they've changed ALOT, my ears would be hard-pressed to tell - my ears are 33 years older, too......
Far as it goes(And that's not far) I've never heard anyone say they've been changed/cheapened over the years...... Costs CAN come down, as manufacturing technique may have improved(Or at least maybe more automated), competition has certainly intensified...
Last I looked the Sennheiser 421 was WAY down in price! AKG C414's are WAY down in price! Same reasons, I suppose.
TG