I agree entirely. I always think of clients first, balanced by server security. Some clients will always want to do something which may compromise the security or stability of a shared server, and I just don't allow some things.
Over the years, I have found that you cannot please everyone, and there are plenty of potential clients out there. The ones which do not want to abide by the limits I impose are free to go elsewhere (like I should give them all root access? no way! go away!)
Server stability is always a nice thing. Fine tuning param screens and many other admin screens of course, would be very nice, cut down on shell time doing manual edits.
Even if Plesk had their own yum repo, the only thing they could try to guarantee is that the contents should not break a box which has no customizations. For example, if you have software AA which has addon module BB, and BB will only work if CC is of a specific version, AA itself does not matter what version CC is. You yum update (from any repo) and CC gets updated to patch some security holes or whatever, now module BB will not work. But AA and CC themselves do work, just the addon CC has a problem. Who's fault is it?
Once you start customizing things, there is no way for anyone (not just Plesk) running a repo to be able to guarantee that nothing will ever break. There is no feasible way for them to account for the millions of ways an admin can change a server which will not cause a problem with a given update. (my view of reality)
How far off topic are we now? hehee