Yeah I don't have them do any script installs or anything like that, just keep my servers up and serving is all that I ask of a host.
That being said I have needed server stuff that required root access like installing ImageMagic and for stuff like that is was done in a few days or less. Most techs don't seem to have very good people skills. LOL
Do a lot of webmasters ask hosts to do script installs? I've always thought things like that were up to the webmaster, same as doing your html docs.
I guess it is about what level of support you want to pay for. If you have a box at a place like the RackShack then you will be lucky to even get someone to hit the reset button, you are basically on your own as far as maintaining your server.
Scripts are easy to install, but I guess that is because I've done so many of them.
Back to your question I believe most webmasters just use one box for all of their domains.