Jailbreaking occurs for dozens of non-pirate reasons, most commonly to allow tethering, or the installation of apps that apple does not like, or to allow the user to use a non-approved network (such as T-Mo in the US).
Also, does flurry now disambiguate multiple devices on the same account? I know I have 6 or 7 devices on my account [I too write apps for a living] alone...but I'm sure I only count as one sale. Seems like those people would also show up as pirates by your metrics.
(I know this is a bit pedantic, but I do want to remind people that not all jailbreak users -- and, in fact, more than half of them -- aren't pirates.)
Flurry tells me the number of [new jailbreak users], which lines up almost perfectly with: [new users] - [new sales].