Greetings:
A closed server system may look trivial from the outside, but I assure you, it's not. In order for a closed server to work, you have to architect the engine to have "no host" execution, which means that the simulator can be run on a remote server, and if you're going to have any significant size of community, you further have to make sure that you can run multiple instances of the game simultaneously on one server. Then you also have to store the data in such a way that all of the characters are accessible (and updatable) on all of the servers; if you segment the population, people will bitch that you don't know what you're doing and complain that they can't play with their buddies half-way around the world; if there's lag in updating data, players will exploit and/or complain to your customer service (about a free service, by the way) that you lost some item or completed some quest, and it didn't register properly because you logged off (or get disconnected) right after doing something cool.
Now, neither customer service nor servers nor bandwidth are free. So, you have to factor that into the cost of what you're doing, as well as the development cost of all these things that you don't have to deal with at all if you're doing only peer-to-peer connections. From the end-user perspective, you don't really have to deal with tradeoffs; you can say that you want X AND Y AND Z, and frankly, that's your prerogative. On the development and publishing side, we need to look at whether X is more important than Y or Z, since we can't do everything we might want on every project (and this isn't just a money issue; there are also costs in terms of focus and time).
So, you know, we looked at the tradeoffs, and we decided that it was more important to give people the ability to create and host custom content. We decided it was more important to get the broad variety of the skill system. We decided that we wanted more memorable boss encounters and more AI types. We could have spent that time working on closed servers, and we could have taken the money away from staffing the art team to fund the servers, and given you much less in the way of items and monsters and animations and length of campaign.
But if we'd done that, people would be on the forums saying "RPG's need to have a certain length to them; everyone should know that this bar has to be met", and no doubt other people would complain that the skill system wasn't deep or broad enough, and yet other people would complain that the bosses just weren't that exciting, and so on and so forth.
It's not that we don't understand that people want closed servers and secure online character data storage. Frankly, we'd like that too. But, in game development, you have to make choices about where the best places to spend your money are, and we chose making the gameplay experience as robust as possible, giving players the ability to make and download new content (for both multiplayer and single-player), and making a fantastic-looking, epic world.
You can disagree with those decisions, and that's fine. We know we're not going to make everybody happy. Hopefully it makes a little more sense now, though, why closed servers didn't make the cut.
Best,
Eyejinx.