Well... the meaning of the BOOL is the same really. If it's a new version (`newVersion == YES`) of Quicksilver, then the version has changed (`versionChanged == YES`)

I'm not quite sure what you're getting at. Nothing's changed... anyway, that line is right:

If we're not running the setup assistant or the version number hasn't changed (i.e. this is a normal launch) then just rescan all catalog indexes as usual. Rescanning isn't the same as wiping and scanning (because the scan isn't `forced`).
If you follow the code that line calls `-[QSLibrarian scanCatalogIgnoringIndexes:NO]` i.e. - not a forced scan.