It's not quite entirely about culture - I do think that a synchronous call with someone provides better opportunities to detect their unknown unknowns, because

It's not quite entirely about culture - I do think that a synchronous call with someone provides better opportunities to detect their unknown unknowns, because you get to see their thought process as they formulate the question. Obviously one can get by without it, but I think this is one of the places where the lack of serendipity actually does hit a little. Once someone has fewer unknown unknowns, though, the act of asking a question by text can often be enough of a rubber duck that they don't need to hit "send" at all.