I may be wrong, but I believe Apple writes their own PDF reading software, rather than use that as supplied by Adobe. That could be an issue with why these types of exploits tend to happen more often on the Apple PDF reader - it's not as tracked as the Adobe official offering.
Actually, display PDF is the default technology to put things on the screen in the OSX Mac world and it makes it dead easy to create PDF or view PDF files on a Mac without Adobe products. It also means that all the vulnerabilities that plague Adobe Reader and Adobe Acrobat general leave the Mac completely unaffected. . . Especially since the data stacks and heaps on the Mac, where such PDF data are held, are all non-execute memory areas. Apple has general NOT been impacted by the exploits such PDF vulnerabilities have opened on other platforms.
iOS, on the other hand, although a subset of OSX, does not use non-execute data stacks and heaps, so is vulnerable to imbedded executable code in a PDF file. That is the vector the Jailbreakers have been using to do their work and the potential, although unrealized at this time, for a malware incursion. Counting this one, that's two for iOS using PDF.