Well, I think we can all agree that the first problem with the site I linked to is that by implication it leaves the impression that it is all right to run multiple resident AV's at the same time. This is of course just asking for trouble. I posted this link to a number of sites, and sure enough some replies took this to mean it was all right.
The so-called combinatorial analysis makes no logical sense to me. I suppose if one ran on-line web (not resident) AV scans it might make some sense. For example, I punched in Avast!, AVG, Kaspersky and Symantec and it came up with a 75% detection rate of near-zero day malware. I presume that means that if I was to run these four AV's sequentially on-line via the web, it would detect 75% of near-zero day malware. There is merit in the idea that once a resident AV finds an infected file, then sometimes running an on-line scan from another maufacturer can help in determining its real or false positive status.
But what I find unforgivable about the site is that it (unintentionally, no doubt) implies that it is OK to run multiple resident AV's and does not explicitly state that this is a very bad idea.
-Bob