[mikerichards]

I think one of Rich Hickey's quotes expands on your point:

It has always been an unfortunate characteristic of using classes for application domain information that it resulted in information being hidden behind class-specific micro-languages, e.g. even the seemingly harmless employee.getName() is a custom interface to data. Putting information in such classes is a problem, much like having every book being written in a different language would be a problem. You can no longer take a generic approach to information processing. This results in an explosion of needless specificity, and a dearth of reuse.

This is why Clojure has always encouraged putting such information in maps, and that advice doesn't change with datatypes. By using defrecord you get generically manipulable information, plus the added benefits of type-driven polymorphism, and the structural efficiencies of fields. OTOH, it makes no sense for a datatype that defines a collection like vector to have a default implementation of map, thus deftype is suitable for defining such programming constructs.