As is usual for Debian, development periods between releases is excessively long compared to other distros. Debian 6.0 Squeeze was released in February 2011, over two years ago, and the team are only just now announcing the date when the current testing version goes stable – Debian 7.0 will be “released” on 5th May.
Debian Wheezy has been under feature freeze for a while now, with a release announcement seemingly imminent for a couple of months now. This announcement has wide ranging affects, as a lot of distros use Debian testing as their base, thanks to its fairly stable and rolling nature. The next testing Debian, 8.0 Jessie, will likely be seen as the new base for a selection of distros before the year is out.
Watch out for major updates to Linux Mint Debian Edition, PureOS, and Webconverger in the near future.