In unix, you normally run as a normal user. But do either "su -" before doing interesting things, or sometimes (for more common tasks) "sudo <task>".

The system asks for a password so if you forget to lock the machine, a bad person can't take too much advantage of the occasion.

The "run as admin" is easy to do, but stops you from accidental file erases - when you don't have the rights you may realize that you tried to kill the wrong directory. And at least the "stupid" virus applications have a tiny bit harder time elevating themselves to a level where they can do anything. And their code to elevate themselves will probably break with next Windows update since the way to "run as admin" probably have moved around a bit.

But it is hard for M$ to first build a complete OS and then later figure out that the "don't do your daily work as admin" rule is quite good. Then it's hard to redesign without breaking a lot of eggs.