Otto von Bismarck said "If you like laws and sausages, you should never watch either one being made." The same could go for a conference program. With some notable exceptions, great papers will be accepted, lousy papers will get rejected. But the majority of submissions fall into a middle range where decisions get made by the tastes of the program committee, not only in area but on whether to emphasize deep techniques versus importance and usefulness of the result. Different PCs make very different decisions and one shouldn't make any conclusions about how one paper fares in different submissions.
On the purpose of STOC and FOCS: STOC started in 1969 because the Switching and Automata Theory (SWAT) conference had too much switching and automata theory and not enough of the newly growing areas of complexity and algorithms. Eventually SWAT became FOCS and followed suit. The only official role they have today is to be the flagship conferences of two theory societies, ACM SIGACT (STOC) and the IEEE-CS TC on Mathematical Foundation of Computer Science (FOCS). What purpose do they play now in a diverse theory community is a good but not well-answered question. So we have kept the status quo where, except for adding parallel sessions, have followed the same basic model since the 60's.
As a commenter has pointed out, the accepted papers list of the upcoming SODA Conference came out last week. I'll leave it to bloggers who care more about algorithms to talk about the good papers there.