Considering the vast majority of computer users and potential Microsoft customers reside in the northern hemisphere, I don't think there's any problem with using summer as a timeframe.
You mean lack of specificity?
From what I gather, it's at some point during the middle of my winter.
Of course, nobody actually remembers when the seasons start and end (though we just check wikipedia), while most people definitely know the order of the months. And even after checking, "this summer", is really a 3.5 month period, which is still as vague (if not more) as "mid 2015".
Of course, in some scenarios it's just impossible to disambiguate.
