I would still race if there was some definition of a standard bike that I needed to buy, but I wouldn't ever be in favor of it. It would be way more trouble than it is worth. Everyone would need their bike examined every race to be sure it abides by the rules (go ahead Doge - chime in about the immense hardship that is junior gearing). I can imagine driving to a race and being DQ'd for any number of reasons - your rims are too tall, aero bars, is that electronic shifting!, are you trying to race with a seatpost that isn't round! cheater! latex tubes! those save watts and not everyone can afford them!
To gsteinb's point - trying to standardize on a 'merckx bike' that anyone would have meant he would have had to go out and buy wheels with box section rims or something, making it more trouble than it was worth.
Also, don't think that this is some new phenomenon and all bikes were equal at some other time in the bike racing. There have always been the innovations of the day that made some bikes faster than others although we didn't have power meters and wind tunnels to measure the savings.