Why is there a need for premium scripts? The tasks that are being automated in Diablo 3 are so minimal that I don't think it warrants premium scripts on top of the premium client.
While this is true, there has been a community outcry of sorts for fully AFKable profiles or ones with premium style features.
An example was BuddyMe's keybot. Up until it's release, there was basic xmls that you could run. None were 100% AFKable and they weren't efficient when they did work. BuddyMe created an entire UI that tracked all of your statistics for keys found, it also used these stats to determine which keys to pursue. After it's release no one used anything else. Due to the amount of time spent managing a thread BuddyMe dropped the plugin for awhile.
toNyx was another example of a guy who took a community outcry and created a plugin for gear swapping. Up to that point, by-hand players had a distinct advantage because they would gear swap to attempt higher levels. toNyx not only created a plugin to change this, he fully fleshed it out with everyone's requests and created a UI to make the plugin easier to use.
xzjv/rrix gave us the new itemlist that uses a UI to change your pickup settings which is 10 times better than the old system. It also allows for the saving and distribution of saved item lists which anyone can paste in, then modify to their whims without ever leaving the DB window.
Community combat routines get posted to provide quick fixes for certain builds. Often times they leave something to be desired... Like a fully fleshed out combat routine that is polished and works better than the most skilled pro gamer.
I could go on, but there is a reason for it. Not everyone would want to pay for it but it would be nice to get a consistently supported profile/plugin/etc that's supported by the same people for multiple patches.