Sorry for not explaining myself clearly. What I meant was that these assemblies are not interchangeable and contain different features. You can still use the 3.5 binary in 4.0 applications, and you should because in it is our LINQ implementation (that is the same for 4.0 and 3.5).
The OpenAccessLinqDataSource is a web component for ASP.NET Web Forms that is used for easily binding data. And DynamicData is a web framework that is used for quickly setting up scaffolding for basic CRUD operation on entities.
You needn't choose between one of the two binaries, just reference them both. I completely agree that the naming here is misleading and this is something we will certainly fix in the future.
I hope this helps.
the Telerik team