COOLDOWNS - In vanilla, prep was a 10 minute CD and the other major cooldowns were 5 minutes. In a battleground enviroment, you really had to conserve your CDs as best you could. It was constantly a matter of making a judgement call as to whether you could win a fight without having to use certain CDs.
BLIND - Blind required a reagent so was a limited resource. If you didn't harvest fadeleaf yourself you had to use the auction house. It was typically expensive and was often not available due to demand. Because of this, blind was often used as a last resort rather than being used aggressively. If you even had it available for use at all.
SKILL - I believe that the game today requires more skill than vanilla simply because there are many more abilities and cooldowns to manage for both yourself and your enemy. With that said, there are certain abilities which took more skill to use in vanilla than now. For example, vanish. For most of vanilla there was no cloak of shadows and vanish was not protected. It typically wasn't possible to use vanish defensively, so it was usually used offensively to get a midfight opener. That had to be timed, because more often than not a rogue would have dots streaming all over them.
Also, it goes without saying, that the overall level of play of WoW players has increased with each expansion.