With Instant Clearing, why PDT in cash accounts?

How can the NASD continue to prohibit daytrading in cash accounts when Instant Clearing is so commonplace? How does the NASD justify their position?

 

because some people still keep paper stock certificates and they need time to mail them in.

 

Maybe because some places don't use instant clearing? Or perhaps there is not enough of a cry from the industry to change the settlement policies currently in place?

 

I think it's a shame, but your answers seem viable....