Yes, but fragmentation goes against cross-platform.
We are starting to see the same problems with Qt, than with other eco-systems (like Android) : the more different Qt versions there are in the field, the more difficult it gets to make cross-platform things, except if using only the lowest common denominator.

Someone who starts to write an application today, will use Qt5.5 on desktop, but would not be able to directly use canvas3D/qt3D/QtLocation/Bluetooth4LE on Ubuntu touch, and a lot less in Qt5.2 on Jolla.

That is what is bad in this situation. On the other hand, not spending all their time to try to follow closely each release of Qt is legit.

About fragmentation, Silica also doesn't help as it can't run on anything else than Sailfish itself. But it looks great