From this : http://msdn.microsoft.com/en-us/library/ms143506.aspx (Hardware & Software requirements) it looks as if you will need both 3.5 SP1 and 4.0....

As Microsoft has been moving towards more frequent releases of SQL Server in the last 5 years compared to the previous 5 years, and given the increased # of service layers in the product (some of which get enhanced from version to version) this is a side-effect.