The answer is simpler than that: MeeGo is not the focus, so they don't want to focus too much energy on this. The MeeGo/Harmattan team is lucky to still exists, so Nokia is not betting too much cards on it.

On the current condition, they could scrap the idea entirely, or bet as much as possible in a single shot, to make it more polished, and easier to develop - so it's obvious with the design choices followed the mainstream crowd to be "safe" (closed battery, unibody, slate design, simple interface, etc)