WTF are you on about?
If you can point me to an OS where the user cannot run an application that encrypts their own files, then maybe your post has some merit.
An application that runs when a user tells it to, and all it does is encrypts files that the user has access rights on.... tell me exactly how on earth any OS is going to stop this?
This isn't a Windows exploit (like the majority of virus/malware infected users) - it's an application that is installed under the pretence of something else. Called a Trojan - look it up.
And there isn't a OS in the world that this wouldn't work on - unless humans are not allowed to touch it.
And regarding your Windows bashing - I want to double check with you... your Ubuntu (presumably as your technical knowledge seems to be lacking) box is plumbed into the internet without a firewall...? If that's the case, you really have little credibility posting here. Any OS - Windows, Mac, Linux SHOULD have a firewall in front of them. It's just common sense and best practice.
Whilst you don't seem to understand the concept of Trojan Horses, i'm going to explain it just to see..... If a user is logged onto a computer with administrator / root access then clicks on a "free screensaver" download - what has the OS done wrong? That's how malware is often installed. Users run as admins (as they prefer convience over security) and then download any old crap. Again - that is not a Windows exploit, but rather a social engineering trick with the payload written/compiled to run on a Win32 operating system.
Vista's UAC (similar to linux Sudu) wouldn't stop this if the user is an admin as they think they are installing screensavers. Again, on a Mac or Linux box the same applies - just get a user with root to try to install your malicious application - simply ensure the app is advertised as "britneynaked.exe" instead of "ransomware_virus.exe".
Very few infections are from worms or browser exploits. It's normally stupid users opening attachments / downloading apps whilst running as an administrator. This has nothing to do with the OS of choice - it's the end user that executed an application without knowing what it will do - resulting in actions that the user didn't want. The OS obeys the users commands and opens the app which encrypts files.
If you need correcting in more simple terms then I suggest a GCSE IT.... FFS