On the contrary, there are companies blossoming based on people doing "let's play". Youtube is filled with partners making incredible amounts of money doing "let's play" videos and frag highlight reels with dramatic music and editing. Any random video garners between 500,000 and 1 million hits within days of uploading them. They become viral instantly. And, their subscriber lists hover in the millions, every one of them sitting through both pre-fill ads
and sometimes interstitials (for 2+ hour playthroughs with commentary).
This market is not niche. It rivals cable TV shows in reach. And, demographically? Forget about it. They are the youngest and money-spendiest one out there. MTV wishes they could pull Machinima demographic numbers per piece of content (and for the price of content, which is an order of magnitude cheaper than the Situation and Snooki, that's for sure).