Building an email list of millions of people seems like a formidable barrier to entry to me. Particularly so when the CPC cost for anything even vaguely daily-deal related has shot through the roof over the last couple of years and is in the $5-$10 range per click now. It usually takes several - several tens of clicks to convert to an email subscription, depending on landing page.
Not to mention the cost of hiring and organizing thousands of salespeople nationwide.
I don't recall precisely, but I believe that LivingSocial & Groupon are still far bigger by market share than the rest of the players put together... that's not what you get in a space where barriers to entry are low.