http://radar.oreilly.com/2010/04/the-ipad-isnt-a-computer-its-a.html
An interesting look at the iPad. The suggestion is that Flash on the iPhone would reduce the exclusivity of the device. Developers working with Flash, if it were available on the iPad/Phone, could be making apps for all of the devices that support Flash. By only allowing Apple approved languages on the i devices apps for the devices will only appear there.
Thanks to James for this link.