- Nokia used to own Qt, so that was the official place to get it.
- qt-project.org is where you will find the open source licensed versions and source code.
- The commercial part was sold to Digia. If you want a commercial license, that would be your location.
Basically ignore the Nokia stuff now, and choose the appropriate package for your needs, whether it is just the libraries, or the complete SDK including Qt Creator and the extra dev tools.