Devexpress is overloaded with concepts and the size of the library is just insane, the latest release is 221MB excluding kitching sink. Compared to jQueries 19KB. jQuery on the other hand focuses on a simple core with just the right amount of abstractions (very lispy), and delegates specific functionality to plugins, such as flot. The difference of course in part comes from the fact that jQuery is an open source project, while devexpress is a commercial project.
You just have to look at the release notes for each of these projects in order to see the difference. jQuery focused on making their already working code faster and fixing bugs. While devexpress spend most of their time added a number of new features. The problem is that in a commercial project fixing bugs doesn’t pay up as well as implementing new features. Or at least that used to be the case. In the era of google that simply is not true. Anyone can put in devexpress and find out if the library sucks (which it to a large degree does) or if it rocks. The sooner they realise that small is the new big, the sooner we will start getting better libraries.