All advertising is about what the next-best alternative is.
It's your device, so you can do whatever you want with it. When you download something onto your device, it is now yours to remix and play with in any way you want – provided you don't republish it and make money from it. (Fair use is the exception here.) According to this basic tenet, if I buy the New York Times in print, clip out all the ads and then tape it back together at home, well, that's my right.
Many a small thing has been made large by the right kind of advertising.
Advertisers go where users spend time.