said by Wai_Wai :

It is because WebWasher uses AntiVir engine in this test, as someone told you in the previous post.

Now why does WebWasher score higher than AntiVir? One reason I could think of is "Webwasher will report every UPX packed DLL as suspicious". Since this testbed only contains malware (no test about the accuracy of the scan result), Webwasher can detect every such malware while AntiVir can't. This may explain the discrepancy.