According to this googled article:
The .NET Framework 4.5 RC is included with Windows 8 Release Preview and installed on your computer with the operating system. However,
the .NET Framework 3.5 is not automatically installed with Windows 8
Release Preview. To run applications that require the .NET Framework
3.5 on Windows 8 Release Preview, you must enable version 3.5 on your computer. There are two ways you can do this: by installing or running
an application that requires the .NET Framework 3.5 (that is, by
installing the .NET Framework 3.5 on demand), or by enabling the .NET
Framework 3.5 in Control Panel. Both options require an Internet
Additionally, according to another MSDN article:
Starting with the .NET Framework 4.5, the Client Profile has been
discontinued and only the full redistributable package is available.
Optimizations provided by the .NET Framework 4.5, such as smaller
download size and faster deployment, have eliminated the need for a
separate deployment package. The single redistributable streamlines
the installation process and simplifies your app's deployment options.
When you install the .NET Framework 4.5 RC, the .NET Framework 4
Client Profile is updated to the full version of the .NET Framework.