The first video test is completely flawed. When Smart Screen and UAC warns you to not run the file the reviewer runs the files anyway. What kind of a test is that? Your your AV blocks a malware would you disable it to run the malware anyway? if so then you deserve the infection.
The second video is more accurate but still don't show the complete picture. If you don't always download files from trusted sources then you will get infected no matter what type of security products you use.
I currently use Windows Defender + Windows Firewall + UAC on my Windows 8 laptop and I have never had one single infection.
Of coarse I always watch what I do, so does Windows 8 default security offer enough protection for novice users? well no it doesn't and none of the other third-party security products will do any better at keeping novice users safe.
Your actions are far more important then what security setup you use.
Is Windows 8 default security enough protection for users who watch their own actions when downloading files and surfing the web? Yes it is because UAC will block any type of threat if you use it correctly and only approve known trusted programs.
Thanks.