I dont see that as a problem with the system as a whole. Its up to you to use this little extra feature (little compared to all the other features offered in the package). This is just an added benefit for those that happen to carry cell phones on them (not a small population nowadays). And as I have seen it, it is just used for switching music/video distribution. This feature does not affect all the other ones (other HA, Asterisk, MythTV, etc.).
I would not be using the carry-cell-phone feature neither because I don't care about automatic music/video distribution switching.
For all other HA functions it offers more/less similar options as other systems (touchscreen, IR, RF, PLC, etc.). No less than what other systems have to offer.
I think it is used for more than media distribution. It says it "recognizes" family members and automatically disarms the security system, sets the lights to the person's preference, turns lights on and off as you move around, etc. I think this is all cell phone GPS stuff and most won't work if you don't carry a cell phone.
I admit that besides reading some of the documentation (several hours, actually) I have not tested a fully functional system (installed/deinstalled within a few days), so I might not have all the details.
However, I understand that a cell phone is used in two ways. First, as a remote controller. I believe that at this moment this function is limited to Symbian phones - for which there are very few models in America. They are supposed to be working in other models.
The second and most creative use is the one that you mention. It uses the cell phone's Bluetooth to work as an RFID. By pairing the bluetooth phone to the closest PC in the house it detects were each person of the house is located. This can trigger any type of action, as you say. But the most unique one - and the one that they demo in their flash presentation is multimedia.
Actually, I wonder if it really needs a cell phone.. After all, it works just by pairing bluetooth devices. Probably any other bluetooth device serves the same purpose without requiring the cell phone part. Once bluetooth earphones get small enough it would be possible to achieve the same results just by carrying a little earphone inside your ear canal. And then you would be able to receive private messages from your house directly to the bluetooth earphone. You could even dial a call from anyplace in your house or send any VR command by speaking to your HA system via your earphone. Several orders of magnitude cheaper than a full house echo-cancellation voice recognition system.