Pingdom stats are a bit strange sometimes. For our services (check my profile if you want to know), a normal month is 100% uptime, simple. But sometimes, your website is marked as down because they have an issue. Several times, we had downtime because of errors between their servers in California and us in Europe where I was able to backtrace them as a network issue deep in California.

So, like any stats, take them with a bit of salt.