There's a reason why advertisers will edit out branding of products that they happen to use in their ads. The most prominent examples I can think of are tire companies. They use recognizable luxury and sports cars to show off their tires, but, if you look closely, they've edited out the logos and nameplates of those cars. Presumably this is to legally shield themselves from those car manufacturers accusing the tire company of misusing their trademarks, or implying an endorsement where none exists. In this case, it might be wise to edit out the Macbook Air and Apple branding, so that it doesn't look like you're being endorsed or supported by Apple.
I wouldn't assume that. It could also be simply because they don't want to give publicity to another brand. For example it's hard to believe that if Coach decided to put an ad with an Apple Macbook in it they would have an issue with that. 
In any case here are the Apple guidelines:
I see nothing on this page which prohibits someone from using an Apple product in a photograph and it's almost impossible to believe that Apple could claim trademark (or even if they could would expend energy to stamp this out) over someone taking a photo of their laptop. In other words a picture of someone sitting in a coffee shop using a Macbook, iphone whatever.
 That said Coach is a large company and they would almost certainly be ritually correct in their approach. Done on a smaller scale the amount of care does not have to be the same.
"However, a French court ruled, in June 1990, that a special lighting display on the tower in 1989, for the tower's 100th anniversary, was an "original visual creation" protected by copyright. The Court of Cassation, France's judicial court of last resort, upheld the ruling in March 1992. The Société d'exploitation de la tour Eiffel (SETE) now considers any illumination of the tower to be under copyright. As a result, it is no longer legal to publish contemporary photographs of the tower at night without permission in France and some other countries."
This info pertains to NYC, I believe it to be correct:
That said, there are plenty of examples in the wild, even in app store screenshots, of violations of this policy. So Apple's enforcement doesn't seem to be particularly strict.