I have only a glancing familiarity with EntityStores (and not much more with DataSets). They resemble object/types to me. DataSets are more how they sound...perhaps repeated instances of a certain data types (though that set of types can be irregular). Semantics of EntityStores would seem to have to bend to apply in the same way. By the same token, DataSets seem much more appropriate for SQL data than EntityStores. I think the DataSet documentation even mentions SQL-like operations in passing.

Thanks for an interesting question. I'd welcome corrections.