My custom frame has a 74.5 sta. Why? because I have a short femur and ideally could use a 76 sta. Even with the steeper sta I need a zero degree seatpost and my saddle as far forward as it can go to get the proper positioning over the pedals.

A steeper sta will put you closer to the center of the bike, I have a mtn bike with a slack sta 72 degrees and I feel like I'm on a recumbant bike. The power that I have closer to the center of the bike is not there on the mtn bike.

Maybe by using a steeper sta the companies can fit a wider range of riders. It is also used for optimal geometry and to prevent toe overlap.

BTW, when I was looking for a new bike I demoed a bike with 700c wheels. I was able to take it on a 10 mile ride with hills. I didn't descend or climb any faster on 700's nor did I ride the flats any faster. I ride my custom bike faster because it handles better on downhills and corners better. 650's accelerate faster than 700's. I keep running into my so when we slow down and accelerate. Riding faster is often the engine, not the machine.