Lol, I put the same question to Xavier barely a week ago. It's not Admin's fault; they generally pick the first thread they see that needs marking, and they don't mean to pass over others. That's why they set up the Call Admin threads so that posts they miss can be brought to their attention. Despite my theories, they are apparently not evil computer programs designed to judge me through the quality of my writing, lol. They are human, and have their own lives and if they miss a few posts, it can't be helped. And I know it always seems like they miss the same people (me and you for example), but trust me, that's just bad luck on our parts.
And as for the first part of your comment, I personally feel Xavier is quite generous to my rather pathetic posts, and Sal is a little more picky with my clearly poor writing, so I guess it varies from person to person. Xav and Sal each have their own standards, and that can't be faulted. At the end of the of the day, they do the job, and they do it exceptionally well, better than a lot of RP forums I've been on.
If you think your posts are being overlooked, post it up on the Call Admin after the 3 day mark, and wait 2-3 more days. If it's still not been marked, politely PM one. But I've not seen it come to that. Just keep posting in the meantime, whether they've marked your previous one or not. Their punishment is the longer they leave it, the more they'll have to mark when they get to it.

I hope I've been a bit helpful

((And yay this is the 2500 message on the forum!!...

))