I do that too. Extending Ember.Object also makes a perfectly fine model. You can mix in things like Ember.Evented to use it as an event target. You can work with Ember where it expects promises simply by implementing a `.then()` method.
This is why I'm saying I think a lot of people fall for the same trap/gotcha as you. Ember Data is totally not necessary to be productive with Ember.
Angular has nothing like ED. There is $resource, which is basically a wrapper around $http to provide some sugar. Not really extensible. But it works. The thing with angular is that the change tracking is transparent, so any simple javascript object / array is fine as a model. That makes it bearable to work with an inferior data library.