How does RegEdit require admins to elevate, but not standard users?

Some programs, like the Registry Editor and MMC, will require you to elevate if you're logged on as a local admin but will run just fine if you log on as a standard user.

That setting is stored as part of a program's manifest, an XML configuration tree embedded in the executable (usually). The requestedExecutionLevel setting controls the app's elevation behavior.

• The default (asInvoker) does not require elevation; if you want to run it elevated, you'll need to explicitly do that by choosing the appropriate item from the context menu. Normal stuff like Notepad uses this value.
• highestAvailable - the value responsible for this phenomenon - requires the best the current user can have.
• requireAdministrator always requires elevation. System management tools like DiskPart use this.

You can quickly eyeball an executable for a manifest by searching for the string "manifest" in it with a hex editor or even a text editor. The requestedExecutionLevel setting will be shortly after the place you find.