com_installer version compare for database schema fixed #2146
Here is the bug report: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32179
I don't know if this needs to be fixed in the fix() task of the installer, too.
If the schema version is higher than the reported Joomla version, the only way to get there is if the user downgraded the file structure without handling the database. It'll only be an issue with having a newer database schema if there are fields that are NOT NULL with no defaults.
Either way, using a version_compare statement is more correct than what's in place now.