The loss of AHP isn't the end of the CM15a however it does loose the ability to use the on board memory capability.
Many using Homeseer, iHouse, PcCompanion and other software haven't used the onboard memory capability of the CM15A or AHP for years now.
I am familiar with HomeSeer, Home Control Assistant, xTension (for the Mac), and several other PC-based automation programs. I agree that they can use the CM15A as a powerline interface, but the real advantage of the CM15A was its ability to function autonomously. I was a beta tester for the never released CM14A, and that was a good controller. Most of us know the CM15A has a relatively poor RF transceiver. And without the ability to download programs, the CM15A pales with respect to my own powerline interface.
Hopefully, some enterprising person will figure out how to download programs to the CM15A.
Here is another PC-based program I just ran across doing a search: http://www.freewarefiles.com/Active-Home-Vista_program_44203.html
I have never used it, but it appears to be freeware.
And here is a piece of info on the CM15A from another fellow who has developed a PC-based automation program: http://www.homedomination.com/cm15a_disclaimer.html
It sound like understanding how to directly interface with the CM15A may be quite a task.
(His automation program is much less expensive than some of the other well-known programs out there. )