It's because the amount of false emails we used to get after forcing updates was rediculous. When we forced an update, any minor issue an admin had was automatically blamed on the update, and they sent us emails blaming the update without actually looking at their problem, relalizing it's something completely unrelated. Since they had a problem, and they had just updated, it was instantly assumed that it must be the fault of the update. The majority of those emails were false and cost us a massive amount of time, when the admin could have simply looked up the problem without assuming, and fixed it himself via the normal means (forum, knowledgebase/FAQ). Unfortunately, that's just the reality of it. It's not as much of a bandwidth/load issue.. although at this point, could potentially be without mirrors. It's working fine with the current setup.
John