Forest Hills, NY
I can understand not expecting customers to buy their own voice modems. They are virtually unavailable at retail.
TWC should have known this and used it as an opportunity for bundling - they should have waived the modem fee for any data customers that are also voice customers.
Making the customer use their own data modem in addition to the TWC modem is really stupid - extra CMTS resources are tied up, another device must be tracked in their billing systems, the device may or may not be supported for firmware updates, not to mention forcing the customer to pay for extra power.
The entire purpose of the "approved list" is full support, which means tested firmware updates.
Before bitching about how much power they use, how about measuring it. You lose more pocket change per year than it takes to run one. If you're that damned worried about it, watch an hour less TV per month.