Last comment about casual users I believe that even this type of users will sooner or later start to look for something to make better use for their expansive gadget, although it might be just installation of new software. I have no statistic on that, but I would say that most tablets are owned by computer enthusiasts or educated people or whatever we want to call them (certainly my mother is a casual computer user, she would never consider spending money on something to enable her to surf on a bus stop) As much as I wish luck to Nokia with selling tablets, i do not think it will change in close future, maybe something for agenda 2015

When you start looking for new software, you very very likely end up on maemo.org as it has the greatest application catalog for tablets. And then I would re-pharse your comment about closed software developers: maybe they are not part of the community now, but they may get interested and in the end community wins. If we are friendly and easy to understand enough, we might get casual contributors.