I'm too young to even remember 90's, not to talk about earlier days. Maybe it wasn't that much about dope (there was dope way before EPO and the punishment for dope was just a mere slap in the hand, ask Zoetemelk for that) i dunno. Maybe because EPO is a lot stronger than anything before and the responsivity to that actual dope was more important than actual abilities (Rominger, Riis, Ulrich, Indurain)? I dunno much about dopes and I'm not that interested in knowing more.
Obviously the coverage is better - TV, GPS, Computers, radio etc. Now you know who is in the break and you can do the optimalization on catching the break while losing as less energy as you only can. The amount coverage and overall checking of the roads limits the importance of suprise factor. It was 1987 when Roche and Fignon(?) attacked Delgado(?) on a feed zone because there was a narrow bridge just before the feed zone and Delgado or somebody else threatning didn't know about the bridge and was badly positioned? I think I've readed somewhere about that or maybe it's just my imagination. I think that lack of coverage helped Delisle to take the yellow jersey from Van Impe in one of the last stages in Pyrenees and be a very dangerous contender to win overall before having a very bad next day.
There is less or no amount of bonus time you can get thanks to your sprint abilities. There's no way guy like Saronni, de Vlaeminck or Maertens can stack up 3 minutes on the rest of GC before first mountain stage. The roads are better so no wet, muddy, gravel roads in the mountains, less cobbles. maybe the roads are partly the reason why you don't need any extra pounds and why sprinters and flat specialists (Boonen, Benoot, other Belgian PR/RVV specialists, German big guys) lose more time than before? It's just a theory, propably a bad one.
Van Springel, Maertens, Roger de Vlaeminck, Kelly, Anderson. They could somehow fight in GC while being pretty awful in mountains and not that exceptional in TT, and it wasn't because the course favoured them. The Tour's edition where Maertens was top 10 was one of the hardest one in Tour's history. How was it going? Maertens lost only like 5 minutes on l'Alpe d'Huez (no slouch of a climb) while Zoetemelk and freakin' Van Impe were murdering each other. The closest thing I can think of nowadays is Kwiatkowski's 11th place overall in 2013 TdF yet still he lost like 6-7mins to Quintana and Purito on l'Alpe.