Product Placement

Apple would want to advertise in this medium because it is subtle, and it gets straight to their target audience. The audience that Apple is reaching through product placement is the the teenage fan girls who are tweeting about Glee, on their iPhones while the show is happening, and are too busy squealing during the commercials to focus. So, it's most effective for them to casually show Finn with a MacBook in his bedroom, or Kurt answering Blaine's text via his iPhone, or Mr Shuester typing away in his office on a shiny iMac.