Why yet another QtWebKit browser?
First of all, Otter is not intended to be such a thing, from beginning it is designed to support multiple backends.
Since Qt5 currently ships only one web engine (QtWebEngine is still in the works, planned for inclusion not earlier that in Qt 5.3) Otter has no other option for now (creating bindings is not a trivial task...), but as soon it will become possible it will gain support for Blink (through QtWebEngine) and maybe others (someone tried once to build Qt version of Firefox, so there should be Gecko binding somewhere...). ;-)
As long time Opera user (since 2004, spending only few initial months using Maxthon etc.) I have some specific needs that cannot be fulfilled by any of existing web browsers.
There will be no entry «Why Qt?», why? Because Qt (while not perfect) is simply the best choice. ;-)