Vendor support should be ubiquitous. If a corporate buyer sees a vendor with only a handful of service locations, he's going to look for another vendor. Organizations want to make sure that their users can get service wherever they may be, especially on the road. Some vendors arrange for extranet support so remote users can obtain access to software and other files from the Web. That can save a lot of time and difficulties on both ends.
Many corporations have an international presence and prefer vendors that are also global.
However, more of it has to do with initial deployment. If a company is opening an office in a new country, managers don't want their employees twiddling their thumbs waiting for PCs shipped from the home office. They want a local vendor representative who can provide the same machine as the folks back home. Vendors that can substantiate claims to international availability have great leverage. As we expand globally, we can be confident our people are using the same devices and getting the same support, everywhere.