Differences between some references in Enterprise Library 2.0 and 3.1

While working with Microsoft Enterprise Library 3.1 I've found there is difference in some references. I was working with DAAB (Data Access Application Block), in Microsoft Enterprise Library 2.0 we was refer to Microsoft.Practices.EnterpriseLibrary.Data.dll in 3.1 and 4.0 you should browse it manually \bin\Microsoft.Practices.EnterpriseLibrary.Data.dll and for some reasons you need to add reference to Microsoft.Practices.EnterpriseLibrary.Common.dll