Here is a simple thought if there are ONLY 2,000 self replicating viruses for the Windows and lets say that OS X has 1 which it doesn't. Then lets convert that into the market shart so 1=5% and windows has 95%=2,000. Well 2,000 divided by 95% = 21 Viruses per percentage point. Which should mean that even though Mac's only do hold 5% there in theroy should be at least one self replicating virus out there but there just isnt.
http://www.sophos.com/sophos/docs/eng/marketing_material/SophosSecurityReport_2005.pdf These are the real numbers there are 114,000 known malware apps for the PC, not one attacks or can attack a Mac, these true numbers break down into 1,200!!! malware apps per percentage point for a windows machine even in the worst case scenario if a mac had (1000)- which it actually has none- then this breaks down in 200 malware apps per percenage clearly giving the advantage to the Mac. Moreover since there are none this bring up well if there should be 1,200 per pecentage point then the mac in theroy should have 6,000 malware apps and since it has none we can figure out the percentage of this possilbly happening which is 0.0083%, and since this is true this shows how the market theroy can not be called true at all.