Must have something to do how these scanners are run and they do not run full heuristic services.
I have run the attached JS file (attached as txt file) against jotti and virustotal and only 1 detection:
Attached is a sample of viral javascript code in harmless txt format,
File size: 3134 bytes name analyse.txt
Filetype: Little-endian UTF-16 Unicode character data, with very long lines, with CRLF line terminators
MD5: 8bb23b26a56874b8464156d6db786542
SHA1: 0ab3b42c33e2255b431feeb39478b3585fa973ed http://virusscan.jotti.org/en/scanresult/14a9ca66dbc05abd15777007cdf820fc9be68fe7
and here Gdata detect… ??? …and also F-secure, using bitdefender engine and i think nProtect since the detection is identical
but no detection on VirSCAN