And what gives these fat asses the right to make that kind of rules? Are the athletes their personal slaves? Seriously, what kind of world are we living in where commercial interests can forbid a talented athlete to publicly use the phone that he or she bought with their own money?
Depending on the fat ass, I'll try to answer your question.
Fat ass 1: IOC. This one is easy. They can do what ever they want. It's their show. Whether we agree or disagree with how they run it is immaterial.
Fat ass 2: Sponsors. Since this is MR and Apple fans seem to frothy with righteous indignation tonight, we'll go with Samsung = All Sponsors. My answer to your question is "due consideration".
Samsung: "We will fund these Winter Olympics, Summer Olympics, and the Paralympics. Athletes need not worry about travel, accommodations, food... they just need to compete."
IOC: "Thank you. In consideration of your generosity we will vigorously defend your brand and highlight it as much as possible, to the exclusion of brands that don't help fund these games."
Regarding the Opening Ceremony. It's only one part of the event. It's not the whole Olympics. Additionally they're saying we will give you a device to take pictures/video during the ceremony. Ceremony over? Use your whatever to your heart's content.
I am going to break one of my rules. Analogies - I freaking hate them on MR because as a group we are the worst on the internet, by a mile. But here goes.
Imagine I am a talented pan flute artist participating in the PFRR. Apple decides to sponsor the Pan Flute Royal Rumble (shout out to WWE coming to the ATV). We have a ceremony. Free hotel, free food, free travel... the works, all courtesy of Apple. I decide I want to video the event. So I whip out my Note 3 and start shooting vids and snapping pics. The PFRR says hey since Apple is footing the bill could you use this free 5S to film the ceremony?
I channel Lana Kane: Yuuuuuup