Not quite. First off, there's a similar argument with the Comcast/NBC merger -- why put ABC, FOX, and CBS content on Comcast? But it looks like the FCC will let the merger go through. Obviously they're not worried, there, and why should they? Comcast customers will continue to want their other local channels, and if they don't get them, they'll go to a competing cable or satellite company.
Second: Sure, Apple "retails" music and movies on iTunes. But what I'm saying is that in order to retail it, an agreement has to be made between Apple and the content providers on how much Apple can sell the content for, how much the labels get, etc. Any musician who signs with an Apple-owned Sony Records would know that Apple would never stop selling their music on iTunes, because of a contract dispute between Apple and an outside content provider. There's a lot of peace of mind there.
iTunes is the 800-pound gorilla in the room. Appx. half of all modern music sales is from iTunes, and more and more movie purchases go through iTunes; you have to sell through them, especially music. If other content providers don't make a deal with Apple, they lose a lot of profit. Read what happened to Rubbermaid when they couldn't get a deal with WalMart in the 90's. Same thing here. Apple would have the leverage, and there's nothing Warner Records or 20th Century Fox could do about it.
Are you asking if I think Comcast buying NBC is a good idea? Happens that I don't. As we've seen several times recently, the cable industry and the content owners are increasingly at loggerheads over how much the cable companies should be paying for content. Cable subscribers are often held hostage -- as in New York, where they won't be able to watch the World Series this year for that very reason (assuming they're interested in any baseball games where the Yankees aren't playing, but that's another story). Put one of those content producers under the same roof with a cable company, and you've only multiplied the problem by increasing the conflicting interests.
Yes, Apple retails, and like any other retailer, they make deals with manufacturers. If the terms aren't right, the manufacturer walks -- to another retailer. Musicians don't drive the music industry, and if you don't believe that, try asking one. They're the flea on the tail of the dog -- when they're lucky. You also forget that not all musicians are exactly thrilled with digital distribution.
Apple and iTunes are big, but not so dominant that Apple can call the shots. Amazon and other music retailers have received deals from the industry that Apple has not. We've seen other signs of chafing. The industry clearly is very keen to not give Apple too much power over them, and so the situation remains quite fluid, particularly for TV and movies, a retailing area in which Apple has not been nearly as successful as music. If Apple becomes not only a big, demanding retailer, but also a competitor -- then look out below. Run this big, risky and expensive experiment just to see what happens? I don't think so.