ISB is not a lower tier school they are one of the elite schools and they have a very serious formal dress code.
The only observation i can make is that "American" schools tend to be more relaxed and "British" schools tend to be more formal.
@inman
Regardless of the dress code, there is nothing about woman's professional/formal dress that would require a lecherous look. A womans blouse and jacket are just as covering (assuming the buttons are buttoned) as a mans shirt and jacket. Your admin just didnt want to deal with confrontation and put time into a thoughful policy.