The installer serves 2 purposes in an upgrade situation...
#1 The installer makes sure the stuff gets installed and does not sit in the customers closet. Afterall we are giving the customer better equipment to aid in customer retention, to enhance their service to prevent them from cancelling in the future.
Case and point, several years ago before Dual Tuner DVR's DISH had a deal with Club Dish where you referred 5 friends they would send you a FREE DISH DVR 508.
My Best friends mother referred 5 friends to DISH and got the FREE DVR 508, she got the receiver and instead of replacing her old model 3000 she put it in the closet to collect dust. Everytime I would go over there, I would ask if I could activate it for her and replace the 3000 and it was never the "right time" so finally I just gave up. Fast forward 2 years later by Buddy moved out from his parents house, we setup a new account and decided to get his moms 508 for the bedroom.
He ended up getting into an argument with his mom, and to this day the 508 is still in the closet.
The point here is that the upgrade might have sounded like a good idea when it was ordered, but leave it up the customer sometimes it will never get done!
#2 The installer makes sure its done right, no point in having a customer screw up their system on an upgrade, get frustrated and cancel!