Development with Qt / QtCreator can be very fast, so that's not the issue.

Generally the learning curve for Maemo development is high, since you need to know linux, debian packaging, maemo API's, toolkit API's (gtk/qt), tracker, etc... The downside of all these open source tools and libraries is that coding style will vary, documentation is scattered and not uniform, and there's not a single development environment that can handle even most of the process (QtCreator / MADDE is going in that direction but they should have been there already!).

Ovi store is also a mess, there's no clear information on when/how/who can publish N900 or when Qt apps will be supported. And I've seen a lot of independent developers complaining about the policies and walking away after spending weeks or months learning the platform.