Yeah, I have to agree with others Marcus. That graph has no relation in anyway to "admitting" bugs. It looks more like the number of either a) vulnerabilities patched, or b) vulnerabilities reported by security companies.
To make this in any way, shape or form "pro-apple" like you're trying to spin it, it would have to show a percentage of total bugs fixed at the bare minimum, or better, percentage of bugs fixed vs the total number filed.
Maybe that information was included in the report, but your article provides none of that supporting information. You say yourself in the article "Secunia's method tracks the number of publically reported security flaws" which doesn't even indicate apple admitted to them.