Desktop Manager might have gone out and found the latest OS version for your device's original carrier. The only thing the vendor.xml file does is make sure a Sprint device gets the official Sprint version of the OS, T-Mobile gets T-Mobile, etc. Other than that there is no use for the vendor.xml file. And since BlackBerrys are by nature completely carrier-agnostic, it's clearly only an attempt by the carriers to keep you using their officially sanctioned OS versions. Easier for them to offer support that way.