Just different designs. What you have is a piston ported engine, which only means that the piston going up and down opens and closes the intake port.

A reed valve engine has the intake port somewhere in the crankcase area usually, and has a reed valve to control the opening and closing of the port. Whenever there is suction, it opens, when there isn't, it closes.

There are pros and cons for both. A reed valve engine often makes a more tractable engine, with good low speed torque. At higher rpms, the reed valve and it's assembly become a restriction to airflow and can hurt top end power.

Just the basics there....

AV8TOR