Keys not registering on the iPhone while typing fast, does it happen to you or just me?
I don't know that I would classify this as a bug.  In OS X, Apple has the Key Repeat Rate setting in the Keyboard preference pane which is a similar idea.  Apple currently provides no way to adjust the speed at which key press (more correctly, release) events are registered globally in iOS.

The ability to type over 70 wpm on the portrait iPhone keyboard is something most of us are unable to achieve, so it's unlikely it would be addressed by Apple.