The fact that this was the norm on single-user Windows workstations until Windows Vista is astonishing, to say the least. How anyone could want that back is beyond me. It enabled malware to compromise the entirety of the computer with ease. No exploits or anything required! Certainly not one of these pesky UAC prompts!
Can you still shoot yourself in the foot with UAC? Yes. You own the PC. You should be able to shoot yourself in the foot, by willingly deciding to. Not accidentally.