There have been a number of reports of the new iPad (and presumably it's the same with previous iPads) which claim that the battery reporting isn't strictly accurate. For example, apparently the new iPad will keep charging for potentially up to another hour after it says it's reached 100%.
Resetting your device will make the device check the battery percentage again from scratch, and this will explain the change in value. At least that's what my guess is. So long as the battery isn't regularly dropping percentage points while the iPad is in regular use, then I'd say that there's nothing to worry about and you're fine. Just a little quirk more than anything.
