This is not a reason to sell, but it can help us understand why the market may stall out now after its remarkable advance. You can only be led by these stocks for so long before the rally becomes very long in the tooth. Action Alerts PLUS, which Cramer co-manages as a charitable trust, has no positions in the stocks mentioned.A Stealth Apple-Derivative PlayPosted at 7:53 a.m. EDT on Thursday, Sept. 13 Everybody loves playing the derivatives for the new Apple ( AAPL) iPhone, and my take is that you are too late for almost all of them, as they have roared into the launch. That's the case except for one. It's a stealth play called Millennial Media ( MM), a nifty little company that just came public, and I spoke to CEO Paul Palmieri on "Mad Money" Wednesday night. Millennial helps advertisers reach people through mobile devices on the Web. We hear a lot about the monetization difficulties on mobile compared with, say, the desktop. However, I am beginning to think it is more of an opportunity -- just an opportunity that's been blown by many companies so far, including Facebook ( FB), because they didn't see it coming. Millennial sure did. It deals only in mobile. It's up against Google ( GOOG), which is the biggest player, and Apple, which also has an advertising-service business -- except this is one of those rare situations in which a company you may not have heard of, Millennial, is actually beating Apple. The major reason for this is that Apple's ad system, unlike that of Millennial, does not support the Droid -- and the Droid is the biggest smartphone product there is. Meanwhile, Millennial supports everyone's system -- and the bigger, better and higher resolution a smartphone is, the more money it will get for ads. So it is a pretty terrific derivative play. Why is mobile not problematic for Millennial? The new cell phones enable advertisers to communicate through video, and mobile video is one of the most successful forms of advertising there is. Advertisers are paying more money for mobile video than they are for desktop banners, and the adoption is just occurring. I believe that, with the trends going as they are, it will be difficult for Millennial to stay independent. It's a wonder that, at $1 billion in market capitalization and 75% revenue growth, this company hasn't been picked off already -- especially considering how so many others are struggling with mobile monetization.