looking back a few posts, i believe he mentions using a 2412N (smartlinc). so he's using intermediate software, it's just that it's on a webserver thats embedded into his plm. or, i suppose he could be circumventing the web interface and using the "direct to plm" tcp port. but thats still only possible with a networked plm (ie. smartlinc).
only other way (that i've ever read about) to interface irule directly with insteon is to use a serial plm connected to a gc-100 or itach, and have irule send it the serial commands via the global cache's rs232's tcp port.
anything that involves a plm connected to a computer will require software in between, even if its just something like tcp2serial.