The problem here is that there are two ways to create a user interface: low and high level (sorry, if obvious).
Both have cons and prons (nice look&feel versus familiar&consistent UI).
On Maemo, there is a strong emphasis on high level UI, using either GTK or QT. So developers are in fact not encourage to use custom button shapes, sliders or other fancy, self made things. A similar situation is with iPhone, where we have guidelines about distance of a button from the screen edge, so all the applications give the same experience.

A totally different thing is the right UI design from the elements. We can use standard buttons and text fields, but smartly. Good spacing, well organized screen, interlines etc. Just not to confuse ergonomics issues with general look thing.