Mrs. Obama has a STAFF of people who deal specifically with protocol issues. Had they done their job she would never have extended her hand. Or maybe she knew and didn't care.
The bolded seems like needless speculation to me. I would agree with you and some PP's if it was a prevalent custom at play in the country. It isn't. Addressing some other PP's, it may not seem like a big deal for staff to brief Obama on not shaking this one man's hand, but we have now taken protocal to a detailed level that would necessarily include briefing the FL on the personal preferences of everyone she meets, not just hand shaking. Should she be told that Diplomat X is rather sensitive about his height so it would be better if she wore flat shoes to any event he's at? And also that Diplomat Z believes the color blue to be unlucky according to her tradition and it should be avoided?
Big issues with heads of state? Sure. Widespread cultural traditions? Sure. Widespread religious traditions. Yes again. Personal preferences that do not meet any of those conditions for everyone she meets? Not really reasonable in my book.