Off the top of me head a couple of things that have changed are...

The amount of racing,Crash you mentioned something on this forum about the amount of week class 3 type races now on metro cards.

I bet the introduction of those races have thrown a spanner in the works of a few systems.

One other thing i think has and is continuing to change is training styles,ever since Vintage Crop won the cup more and more trainers are waking up to the fact that all their horses arent the same and they need individual preperations,that could include racing a horse fresh every single time it races,a punter who blindly follows the 21 days since last start rule will be missing more winners.