This saves the systems folks from loading and testing the software themselves before handing off to the employees. All this preconfigured software isn't worth a whistle if a product line changes or, even worse, ceases production. Corporate buyers like product lines that don't change, which seems counter to the vendor tendency to constantly tweak and fiddle with machines in the never-ending race to be, momentarily, the best. You can't blame them. Every component change means another driver to keep track of, another wrinkle in service and support, another potential glitch to bog down IT staffers and rev up the cost meter.
Stability is important for other reasons, too.
One goal of a successful corporate PC purchase is to minimize the impact on the user. Ideally, the employee should be able to start using his new machine as soon as he gets it, with no down time or lost productivity. This implies minimal change for the user. The more the new computer looks and acts like the old computer, the better. Most buyers are shooting for a low learning curve and a simple migration.