Releasing code to CTAN means that it gets installed first on one of the two 'master' nodes: Cambridge (UK) or DANTE. The new material is then copied around the world to the network of mirror servers, a process that takes a little while. The TeX Live 2013 release was made on 2013-06-18 to the Cambridge master node. My 'nearest' mirror (Oxford, UK) updated by early on 2013-06-19, but it is 'close' both physically and in topology terms to Cambridge, so others may be slower: give it at least 48 hours.
To check which version you will download, you can look at the file date in the listing. The final testing build of MacTeX was made in late May 2013, and the
MacTeX.pkg file for MacTeX 2013 is dates 2013-05-30. For the 'standard' TeX Live, you can tell if a mirror is up to date by checking the date of of the
archive folder inside
[archive]/systems/texlive/tlnet/, which again shouldbe 2013-05-30 (or later).
It's important to note that the 'release date' for TeX Live doesn't mean that every file is updated on that day. The final phase of testing is more or less people using the 'hope to release' code and making sure it works, so testing is done when there is no need to make any changes. As such, the file dates for the 'gold' version are always before the release date.