Walled gardens are the future of gadget design. 98% of the mass market just wants to consume, without getting exposed to crud and malware. For them a walled garden is ideal; openness invariably leads to Bonzi Buddy and Comet Cursor.
While there are occasional apps that aspire to such, the fact that basic OS functions are private APIs and are not distributable on the only widely available vector into devices prevent malware and many (but not all) privacy breaches.