It's not just about the size of the sale. It is also about what you are selling and how critical that is to the company's day-to-day operations. If your code review tool goes down for a few hours, meh. If your email goes down for a few hours, the world is on fire and somebody is losing their job.

In the later case, companies want to feel that the "if" scenario will never happen. It's not that outages can't happen, but, rather, that if an outage occurs, you will be taken care of. If UserVoice is your only support tool, you are unlikely to give that feeling.