The virus writers that wouldnt want to take advantage of the user base on macs are the ones that want to create an atomic bomb and not a bee sting. In other words 99% of them. If you could write a virus in 5 minutes than yes i can imagine your point may make sense but the amount of time and effort which goes into it is a lot greater.. Imagine someone asked you to do a huge amount of work and said youd get a million bucks if its a success.. Then the next day someone comes along and say hey i need you to do the same work but you are only gonna get 10 grand at best.. Of course you wouldnt be half as interested and youd go back to the million option.
"The reason for this is that there are no obvious ways for virus delivery and spread."
Do you honestly believe that Bill Gates with all his money and legions of ass kissing coders somehow cant find an elusive twist in an OS that prevents a virus happening and Jobs has been able to find this ? That is total fantasy land. Again, this gets back to size, you got millions of people running PC's that have millions more options and millions of people writing little shareware programs, and with that comes millions more problems and hackers and millions more everything. Its just the way it is.. If there were 10 people on this earth chances are we wouldnt go to war at all, but given there are 10 billion its a lot harder to manage.
The other thing which may not be obvious here is, the biggest majority of computers playing important roles are doing so on microsoft products, therefore of greater appeal when you seek to do damage.. If apple had 5% of the market but all of that share controlled credit card transactions then yes the target would be far more worthy for a virus writer. But the majority of them are in auido/video and graphics or home users which at best might shut down a few studios for a day or two and thats it.. Pretty weak by damage standards for a hacker.
As i said, i have no allegiance to any system.. My argument isnt a knee jerk emotion thing like so many pc / mac arguments seem to be. This **** turns into a game of football half the time, but I couldnt care less which system is best. I bag pcs just as much when i see things i dont think make sense about them.