Thanks for the replies guys.

One thing I need to add is that the power valve was stuck in the open position when I **** it open.

MG would that cause the piston to wear out prematurely?

The power valve being stuck open will not cause the piston to wear out prematurely.  Dirt getting past the air filter and not putting enough oil in the gas for your riding style are the two things that accelerate piston wear.

The power valve being stuck open will cause a loss of mid range and high RPM power.  Running the engine at high rpm with the power valve stuck open can force the engine into detonation and result in burned pistons and or piston seizures. 

The piston pictured in the 1st post probably had cracks in the corner radius of the transfer cut outs before it had 20 hours on it.  The cracks in the middle of the intake skirt is very common when the skirt is modified.