You have a really rotten view on the creative industry I assume you are not a part of it, otherwise you would think differently.
Its a passion driven industry, an industry easy to take advantage of. People take incredible financial risk and abuse (in the form of months of crunch, working weekends) to be a part of it and stability is not a part of this industry. The average time span of people working at one company before moving on to another is 2 years and we keep doing it, no matter how many projects sink, how many studios fall, we keep trying and trying, because making games is an incredible experience. We are glad when people like yourself enjoy the games we developers make but don't come in with that crap you know nothing about.
Yes creative control is important for developers. Its not this face of a company, its hundreds of people who spend a large part of their time away from friends and family to create and realize a vision of something cool. something people will enjoy. Having creative control is the most important deal for developers. (why the hell do you think there are so many indies, a lot of them forming from ex big studio developers) Its the reason bungie bought themselves back from microsoft in order to make a new IP, an IP that they creatively control, something they own. Activision is the publisher and so there is a real reason to get upset when they try to get a hand on the creative decisions done with the game.
A trailer like every other piece of media are as much a part of an IP as the game is and are as important in shaping the vision of for example destiny. Its how people perceive the game beforehand and if you do not paint a picture that is accurate, then you will get a backlash. (ubisoft I look at you). So in this case, having music from the game for the trailer is important. He had a legitimate reason to get upset since his music is a vital part of the game and when they replace it for generic stock music it just fucks up a trailer and make people wonder, "what the hell happened to Marty, why does his music sound so generic as fuck, where is this musical theme of the game, the same type that made me fall in love with halo.