My mac has been online virtually 24/7 for at least 5 years now, with no AV software, and I've never had a problem. It's seen its share of shady porn sites too.
(whereas I've had PC's with AV software still get a virus and fuck the whole machine)
A couple times it's asked me for permission to install some kind of malware. On a windows machine it would have already auto installed. On a mac, you can get a virus, but you have to be such a frikken moron to see the permission window come up and type in your login to say, yes I would like to install this virus.
They make it, because people coming from windows will buy it.
A unix box is just as vulnerable as Windows and sometimes even moreso. If you were pissed, in a country that was repressed and wanted to make a statement, what would you make the statement on? Something that has a large footpront or something with a small foot print on society? If you were going to create an exploit for something that could potentially reward you monetarily, what would you make the exploit attack? Home user Apples at a small market share or a huge market share of business machines and home users combined?
A MAC is simply a modified unix operating system over PC hardware. Everything that man creates can be reverse engineered by another man, and to say it can't is simply arrogant and uneducated.
Things that recently hit Windows more and more within the last few years is something called a rootkit, which is a kernel level driver that makes the operating system basically ignore the malware files themselves. Unix had rootkit malware for over a decade before they ever even hit Windows.
As for buffer overflow exploits they hit Unix kernels almost 2 decades prior to Windows.
Now, if by chance MAC gets more popular and gets more of a market share, AND here's the key, business machines, I'm sure you will see more and more exploits.
A little history lesson; people used to say the same thing about VAX being better when comparing to Unix because of exploits because its kernel was one of the best designs ever made. VAX created by DEC was one of the most stable operating systems of all time, both hardware and software. To this day, VAX VMS never got as much of a footprint as unix held. Solaris, another form of unix from Sun took a huge footprint on the marketshare back when VAX was popular. In the end, anyone that has worked in a huge IT environment, will tell you that VAX was arguably the most stable computer system ever. VAX systems sometimes were not rebooted for over 5 years at a time.
Why do I tell you this? Well, the man who engineered VAX and coded its operating system was the guy that Microsoft hired to architect, engineer, and program Windows NT operating system, including the kernel. The Cutler that really made a difference in the world, not Jay.
While many people think that NT was named NT to stand for "New Technology", because Microsoft had New Technology written in text when the operating system booted, it was actually named NT because it was programmed over the codenamed NT10 or N-Ten processor at the time. This is still the kernel, security, and file system basis/derivative for all Microsoft NON DOS based (Non DOS based = Windows 95, 98, 98SE, Millenium, etc) operating systems including Server 2008R2 and Windows 7. At this point NT is 18 years old and Unix is 41. Problems have been found, confronted, and remediated on Unix in the past as well, which of course tightens it's exploitable baseline. Fortunately for Unix, it was prior to mainstream malware making the news and population of home users.
In finish, don't be so narrow minded to think that an OS derived from Unix that is less than 10 years old in a world such as we live in will not sooner or later have its exploits pointed out if it does gain a valuable foothold on the marketshare that becomes appealing to malware writers.