Was that the question? I thought the question was JetDirect vs. IP printing.
The main reason to use the JetDirect protocol and software is it allows you more functionality for the HP printers; like seeing paper status, ink/toner/consumables status, etc. whereas printing to an IP address using LPR will just print it. Period.
Just my 2¢
"In order to start solving a problem, one must first identify its owner." --Me
--Greg