No, it doesn't require complex clients. There aren't many examples because (1) most developers don't even understand the concept and (2) it reduces lock-in, which most providers aren't interested in supporting.
You really don't think that a flexible client which is able to discover resources and actions based only on an initial URL is more complex than one which is more hardcoded to a specific implementation and resources? I must be missing something, because to me, it obviously is.
The obvious example of the Web and web browsers is not entirely convincing to me. Yes, browsers are flexible, but at the same time, the Web is an incredibly specific example. There are "hardcoded" expectations of what a web browser must be able to do, that I simply don't see in more general examples and use cases. And whenever we want to do something out of the ordinary with a web browser (I know, I know, "web browsers were never meant for that!") this general model of the web breaks down and we stray into wildly incompatible and hacky ways of doing things.
