KDE Developer beineri writes in blog about the general confusion among people between KDE 4 and KDE 4.0. To quote him,
The last feature release of KDE is just over a year old, is well maintained and gains selected features about every two to three months. Still people long for the first release starting with the number 4 often called “KDE 4” – which is wrong. Let me try to disambigue: “KDE 4” refers to the whole life-time of the KDE 4.