From what I can see, the Microsoft Security Essentials score is to be expected with the antivirus software coming preinstalled with Windows 8.1.
Basically, it does not make sense for Malware developers to release Malware they know is going to be caught by Windows' own security software. Otherwise just about everyone relying on the default protection in Windows 8 is going to be immune to the infection. I'm sure it's a similar story for many of the popular free products as it's just a matter of the developers installing AVG, Avast, etc. on test machines and tweaking their Malware until it comes up clean before distributing it.
As I receive a fairly steady stream of viruses by e-mail, it is interesting to see what products catches them in VirusTotal. A few products appear to be checking the icon (e.g. executable with Adobe PDF or Ms Word icons) as a few now show "Fake Doc" as the result and many of the infections now are using blurry or slightly distorted icons as a result.
One security improvement I would like to see in Windows is it to always show file extensions of executable files, similar to how it always shows file extensions of unknown file times, regardless of the "Hide file extensions..." setting. It should also show a warning when opening executable files from a Zip file in the same way as opening a downloaded executable file.