MS assumes that anything that tries and access areas that are restricted can not be truly innocent.
Read this: http://www.crn.com/software/207100934?cid=CRNFeed
In a Thursday presentation at RSA 2008 in San Francisco, David Cross, a product unit manager at Microsoft who was part of the team that developed UAC, admitted that Microsoft's strategy with UAC was to irritate users and ISVs in order to get them to change their behavior.
"The reason we put UAC into the platform was to annoy users. I'm serious," said Cross.
There you have it from the horse's mouth: It was intended to be annoying, in an attempt to get software creators to follow the Vista way of doing things or risk pissing off their users. It seems like Vista itself caught more of the backlash than the 3rd party software creators did, so it didn't completely work out for MS.