The thing is, celeb ads are not what attracts people to the system. Celeb ads attract grass hoppers - not a loyal customers... and if you think of gaining market share you need those. Sure some of them might become those loyal customers but other than that there are dozens of better ways to gain those. One of them is improving the system itself. iPhone didn't grant popularity because it was iPhone and celebs used it. iPhone started to gain worldwide popularity arround 3GS kicked in when iOS gained bacis functionality and AppStore supplemented where iOS was lacking. Right now WP8 is something like iOS 2 (albeit more advanced, WP still lacks some basic features and that was the main reason of this comparision) - hopefully WP8.1 will adress a lot of basic design issues that are bothering the platform as well as MS expands API for developers to create more advanced apps providing deep system integration with other services.
People that work in marketing constantly forget that while for some people it might be nice to use stuff that their favourite person is using, vast majority won't use something that doesn't suit their needs - and guess what's the answer of some random person asked why she/he won't jump onto WP is not "because it's not Apple", but "it still lacks" (or "it's closed ecosystem and I preffer freedom of Windows Mobile/Android approach" but then again there's NOTHING that would bring these to WP as it is). Which in other words means that they like the design and consider moving over once it's finished. And as former Nokia Lumia 800 user (and L920 and now L1520) I know how much it sucks to be paying for being a betatester - but I simply want for the platform to succeed as it's greatly improved experience over iPhone (which I were using prior to WP devices, and earlier than that mentioned Windows Mobile on HTC).