The cable boxes are generic and used by many companies. They often have features that are not used by one or another.
HD boxes do have DOCSIS tuners in them, but it's generally unused. Some of the newer special features may start using it. It's possible, but VERY unlikely that Comcast would add something like Netflix to some future software. If they did, they'd probably charge a big fee in addition to your Netflix subscription, and probably require you to be a triple-play subscriber!
The MOT box has an ethernet port. If the response is the only answer, then it would seem that MOT/Comcast are deliberately downgrading potential "cable TV" service capabilities by making the box unable to receive streams from Netflix. As a Netflix subscriber, I will NEVER buy Comcast pay-per-view streams. So this is pure and simple "squeeze the customer" which smacks of old-sstyle cable operations. Phooey.
You need to purchase a 3rd party device such as a Roku, WD Media Player, Apple TV if you use Itunes, or similar media player device. It would hook to your TV and home network router to stream from the internet.
You can find these media player at Wal-Mart, Best Buy and similar electronic stores.
A Comcast cable box can't stream Netfilx as it would be in direct competition with their offerings.