<i>Are tightly closed environments like this where we want personal computing to go next?</i><p>No point even asking questions like this, until you address what to do about the millions of idiots who click on every attachment they get and answer 'Yes' to every dialog without reading it.  Because social efforts have failed to fix this problem, it's apparently a technical one, and the technical solution is to make it difficult for all but expert users to treat new mass-market devices as wide-open platforms.<p>Sucks, but what else can they do?