Everybody needs to chill out, there's a big misunderstanding here.
By default, all programs are NOT given Admin rights. If it's not called install, it will be "let through" in the sense that it will run as non-Admin. You have to log out and log back in to run it if you need Admin privileges.
This is a convenience feature that has been around since Windows 2000: If you run a program called install.exe (or was it setup?), it will prompt you for the password.
I know that Windows 2000 exhibits this behaviour because I have Windows 2000, and I have seen it do it. Any program named install will prompt for the Admin password. It's a convenience method.
"They will rename their Trojans _to_ "install", because now Vista will helpfully ask the user to run their code as an administrator"
This is true. Linux has this same feature in fact.
In Fedora, if you click an RPM, it will simply prompt for the root password and install it. It would be extremely easy to deploy a spyware this way.
The only reason it doesn't happen is that spyware and adware companies are in it for the money and there just aren't enough Linux users to bother.
You can say security through obscurity is a myth all you want, but for spyware at least, there's at least a dozen ways to penetrate Linux and in fact the same tricks that work in Windows can work on Fedora and Ubuntu, among others, and including the derivitives.
This is one of them.