In Sitefinity v. 3.7 SP4, there was a release version for .NET 3.5 and .NET 4.0. That was especially useful since you could then use whichever version of Sitefinity that supported the framework you were running.
However, with every release of Sitefinity since v. 4.x, there is no .NET 4.0 AND .NET 4.5 release.
This is quite problematic because development cannot leverage the new features in the Telerik .NET 4.5 assemblies and are instead stuck with the .NET 4.0 assemblies.
As with the Sitefinity v. 3.7 SP4, release, Telerik should release versions of Sitefinity that support .NET v. 4.0 AND .NET v. 4.5, rather than just the single platform of .NET v. 4.0 which is simply TOO restrictive.