Despite all of the reasons given, Flash represents a threat to Apples control over the iPhone experience and its revenue. Flash is a platform unto itself. Video at sites like YouTube is on flash and so are thousands of games at sites like Hall Pass and basic apps like a snowflake maker or picture editor at Picnik.
Add to that there are thousands of developers for the iPhone and more than a few would be willing to jump ship and cut their ties with the App Store to develop applications that bypass Apple's review process where the guidelines are less than crystal clear.
Flash provides a platform for many of those apps. I think that is the real reason Apple wants to prevent Flash from being on iOS devices - they lose control. Flash apps can be downloaded from any website. There is no installation necessary.
If you want to install Frash on your iPhone, full instructions are here. Be forewarned though, it involves jailbreaking. Jailbreaking is totally legal, but Apple has the right to void your warranty if you do it.