We’ve detected an issue with download statistics that affect all add-ons and versions uploaded after 3/10/2010. Add-ons uploaded before this date continue to accumulate the correct statistics.
To stay up-to-date on the status of this bug, please follow bug 552162 in Bugzilla.
UPDATE: This bug has been resolved and statistics should be normal again. If this is not the case, please let us know in the bug mentioned earlier.