I'm no longer with the company, so I may be out of date, but the consensus was that it was just too expensive to support licensed products if it weren't necessary. The thing that people don't take into account is that there are an endless number of server configurations that can screw up the application, and for a small company, dealing with each one of those is quite expensive.
So what's the alternative? Keep it hosted-only. The downside is that, yes, outages like this happen. But I would argue that, on the whole, the overall Trello downtime has been far less than the cumulative downtime of people trying to run it themselves. Moreover, this was an extremely unusual storm. Buoys reported waves 5 times higher than anything on record. My guess is, the cost-benefit analysis is still solidly in on the side of having a hosted product in an easily accessible data center.
