The first article that you pointed to claims that "Leap-A" was a virus. That is false. It was a trojan horse. There is a significant difference between viruses and trojan horses. Viruses can be installed and executed on a computer with no user input. Trojan horses rely on users doing foolish things. Leap-A was one of the amateurish trojan horses that I previously referred to. In order for it to do any damage, a user would have to knowingly download the program, knowingly execute the program, and knowingly enter their password. These types of trojan horses never do any real damage and no operating system can protect users against their own foolishness.
The second article you pointed to listed a bunch of routine security concerns going back nearly 10 years. Few, if any, of the concerns listed are considered to be actual security risks. Instead, they are theoretical risks that are unlikely to expose the operating system to any real threats.
I will again point out that even with that long list of security concerns that you linked to, and despite a small army of hackers who would like nothing better than to be the first person to create a virus that affects OS X, the total number of actual Macintosh viruses in the wild is zero.