It is always beneficial to consult the "ignores_qtgui.csv" file in the build directory. It lists all function which were not bound by lqt, and the reason for that. A quick "grep createIndex ignores_qtgui.csv" gives this:
QAbstractItemModel::createIndex;unkown argument type;void*
This means that lqt does not know how to translate "void*" to a Lua type. If you know a sensible way to do that (maybe using lightuserdata?), you can update generator/types.lua and add a definition for void* type.
Unfortunately I currently have no time to maintain lqt. All my attempts were halted because of Qt 4.8 and its threading model, and I currently have no time to devote to lqt. I will get back to lqt early in summer when i'll have a bit of free time.