Sorry, if i don't make any sense. Here's what i am thinking, the malware is lurking in the SUA because user ran it in the first place, which he will do in the admin account also if wishes to. So what's the difference for an average user?Problem is this: there might be malware lurking in the background, just waiting for admin permission to come along. So if you type in the admin password in your SUA, you just granted permission to that lurking malware.
But if you switch to your admin account, that is not where the malware is running in the first place. So it won't receive permission.