Why would you need an explanation? A 15 minute downtime is easily explainable by a hardware failure or something similar - they don't need to alert their thousands of customers every time a little incident occurs.
I'll have to concur that it can be explained by a number of events. An alert for a few minutes of downtime is not really necessary, probably takes more time drafting and sending the alert than the total downtime. I'm extremely happy with them. If I so desired, I'm sure I could get an immediate reply as to what happened. Service has been exceptional.