Why hasn't the World of Always On arrived?
The ingredients are all here, and they're cheap-as-chips: (An example is this nifty little camera, from yoursecurity.us.)
I'm convinced the hurdles facing Always On applications aren't technical, and aren't artifacts of the market.
They're political.
Let's run them down, shall we?

The fact is that Always On applications will create a ton of data out of your daily life. RFID inventory applications will create a record of everything in your home. RFID security applications will put everyone in your house under constant surveillance. Always On medical applications will find out what's wrong with you, before you know it's wrong.
Unless consumer rights to this data are paramount in our law, unless there are ironclad guarantees that the data you create is yours, people just won't create it. They'll continue dying young of heart attacks rather than monitor themselves. They'll continue to waste energy, water, and live in dirty air rather than create the data needed to change things. They'll risk death rather than have cameras in their homes.
These are not market problems. These are not technical problems.
These are political problems. And until we have politicians with the courage and foresight to stand for consumers in these areas, consumers will remain outside the Always On loop.