While I can't specify Diago's reasons for deleting it, I can only refer [you to a similar discussion on MSO](https://meta.stackexchange.com/questions/51097/the-great-question-deletion-audit-of-2010)

While I pity your loss of badges, I don't think that popularity should be any reason to bend or break the rules. So if a question that violates our current FAQ is brought to our attention, it is dealt with. 

I think I must emphasize that last part, because it means the mods aren't out on a witch hunt to bring down our wrath on off-topic popular question. You were simply unfortunate to have your question run into Diago :-)