First of all V21 HAS been released, go on the blockland.us website and go to Download section, it will say "v21". If you still won't accept that, then I don't know what other loving stuff you will accept. You might as well just isolate yourself and be the only Blockland player thinking V21 is still to come. If you haven't realized yet, versions such as 19, 20, 21 occur whenever there is a large change or something bigger than bug fixes (v20 being the the launcher being added and then v21 the removal of terrains and addition of shaders). Anything else that is minor such as bug fixes or more gamemodes being added are Revisions, otherwise we'd probably be up to V30 by now or something.
Understand? Basically it's the Version number and then Revision number on top of that.