For what it's worth, here are some links about UAC.
Starting with Windows 7, certain executables auto-elevate (no UAC prompt under the default setting). They pretty much have some common characteristics, such as being digitally signed, are located in %System32% and/or are instanced from a trusted Windows executable.
This includes your Control Panel, Admin tools, and such. For example, if you download the Remote Admin Tools fro Win7 SP1 and install Hyper-V Manager, you'll notice that while it is instanced from a trusted Windows Executable (mmc.exe) it still gets a UAC prompt despite being very similar to other Admin tools, like Services.
The key is that Hyper-V manager (virtmgmt.msc) is installed into Program Files. Move virtmgmt.msc inot %system32 and UAC prompt disappears.
But to move the file in the first place, you need Admin credentials. So not really a security hole. It's the equivalent of saying that if you sudo a process it can run amok on your system and thus it is a security hole.
My guess as to why this was added in Windows 7? Because some many people complained bitterly about UAC. So much for better security.