In the case of Apple, which I know *you* are specifically referring to, I agree. AntiRepublican and HAL are constantly trying to claim many of the same benefits Apple users enjoy automoatically apply to Linux as well, you see them trying to lump the two together constantly. It doesn't work that way, OSX from Apple and Linux from Red Hat for example are completey different products, install methods, and upgrade processes. Linux, unlike Apple, rarely comes preinstalled, and often patches for Linux have to come from the original vendor, not typically being modular or directly available from 3rd parties. So in your case with regard to most Apple, I agree, but when AR tries to claim that holes aren't in a linux distribution, he is wrong as a patch for that specific distribution is often required.
Since when? The only real thing they have in common is a UNIX-flavored core, which automatically gives them several advantages over Windows. Aside from then being able to use the same UNIX utilities, the differences are quite drastic between OS X and Linux.