Flawed methodology
From VirusTotal's own website:
"Those who use VirusTotal to perform antivirus comparative analyses should know that they are making many implicit errors in their methodology"
In a nutshell, it ain't a real world test, as VirusTotal does not (and doesn't claim to) mimic the protection that users would experience in the real world where they may have multiple levels of protection, cloud-based lookup, runtime behavioural analysis etc etc..