Hi and welcome to EI

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Your post is very well thought out and I agree with with you that all the features you list would be great additions to the iPhone. Some of them may even be available from the beginning.
* The iPod application includes a handy volume control slider, but does not appear to include a method for changing the playing location of the current audio track (rewind/fast-forward/jump to point). This feature does appear in the video player.
I noticed this too while watching the keynote. I listen to a lot of audio books and this feature is a must. I would be surprised if it is absent.
* Flash videos supported: At present, iPhone seems only supports mp4, h.264, mp3, aac. If it supports Flash files, iPhone will be more popular. Flash is working its way into all of todays popular sites (YouTube, MySpace, Google Talk (web), Yahoo! Messenger (web), etc)
Flash may be present from the start. According to an
interview with Steve Jobs, youtube support will be at the very least. Here is the relevant part of the interview:
Markoff: “And what are you thinking about Flash and Java?”
Jobs: “Java’s not worth building in. Nobody uses Java anymore. It’s this big heavyweight ball and chain.”
Markoff: “Flash?”
Jobs: “Well, you might see that.”
Markoff: “What about YouTube–”
Jobs: “Yeah, YouTube—of course. But you don’t need to have Flash to show YouTube. All you need to do is deal with YouTube. And plus, we could get ‘em to up their video resolution at the same time, by using h.264 instead of the old codec.”
* Third-party software: The list of applications available for Windows Mobile and Palm is huge! I am sure many of the Mac developers out there would love the opportunity to develop/sell applications that run on the iPhone like games, video conversion, DVD to iPhone software, music data recovery, media editor, etc.
In a recent interview, Steve said that they still haven't decided if they are going to allow 3rd party apps. IMHO, it is just a matter of time. If I had to bet, I would say they will wait awhile to allow 3rd party apps. This will give time for the iPhone to establish a reputation as a solid stable device. Then if stability problems occur after 3rd party apps are introduce, it will be obvious where the blame lies.