Hey, welcome back! Good to see you.
However, the falacy in this "summing up" is this erroneous statement and conclusion:
The big difference is that actual exploits of Mac vulnerabilities have been extremely rare, and that suggests a lack of interest by attackers.
The fact is that, discounting two trojan programs that hit a couple of greedy Mac users who thought the 300K file they downloaded, installed and executed was a pirated version of Office for Mac, the "actual exploits" are non-existent. A couple of proofs of concept that demonstrated some possible vulnerabilities that were closed within a couple of weeks of exposure, like "Opener" or "renepo", might be added to the list but they were not "actual exploits".
...and Windows, with 90%-plus of the market, is where the money is.
Money. They say that Money is the root of all evil. Think about the lure of 17,000,000 to 25,000,000 TOTALLY UNPROTECTED Mac users out there (who obviously have more money than sense according to PC users because they buy expensive Macs) who are vulnerable to a new viruses and spyware that could steal their identity information... and it hasn't happened. Gee... I wonder why not.
Actually, it is the "love of money" that is the root of all evil. (1 Tim. 6:10) Money is still OK.
Cheers! CC :)