UAC did not deny your install. UAC has nothing to do with it. UAC, in terms
of the elevation prompt, is only invoked if (a) an application asks for it,
or (b) if an application is automatically detected as an installer, or (c)
you have told the OS you want that application elevated. In this case,
neither is true, but you tried to perform a privileged operation
(creating/modifying a service) so the security infrastructure in the
operating system denied it.
The only part UAC would have played in this is that it strips the
Administrators SID out of your token, without which, this operation fails.
That is why you have to elevate to perform administrative tasks.
UAC does not include the vast majority of security infrastructure in the OS,
so blaming it for poorly written software or failing to understand how the OS
works is not a productive way to solve problems.
Your question may already be answered in Windows Vista Security:
> I do lsf installing on Vista, UAC is enabled, type "lsfmon -install" in
> command line and will call OpenSCManager(), there is no dialog box
> displayed and give error "Access is denied". If I turn on the feature
> "Run this program as adminstor" of lsfmon.exe, there is no problem, so
> I want to know why Vista do not give out UAC dialog box for elevation.