It's not supposed to do it every time. It should do it only if the previous update has failed, if the catalogs are older than 24h or if the hildon application manager has done an update and changed the repo settings (system autoupdate in the background can do this). As a workaround you can use the "remove apps" shortcut in the main menu and then change the status filter, it bypasses the check. I'll add an option to disable the checks in the next version. What does your log show after updating the catalogs?