Since 2.6.2 the online manual is not being updated:
http://texstudio.sourceforge.net/manual/current/usermanual_en.html
Though it is linked on the homepage etc. Without it, you really can't find out why you should download and install a new version, as you do not see which new features were implemented or which bugs were fixed etc.
(I found that the manual that comes with the installation is up-to-date)
I've updated the online version