I think there's two basic answers here. The iPhone had a list of "must haves" and a list of "can wait until after launch". On the list of "must haves" were everything... and I mean EVERYTHING that we were presented at the January keynote. Whether in icon form or alluded to, EVERYTHING that was a part of that presentation, was what Apple concentrated on delivering, alongside issues of system stability, performance, and easy of use. A number of things regarding the UI changed slightly between the presentation and the launch. The ONLY thing presented at the January keynote, that apparently ran into unexpected problems, were customizeable ringtones.
Regarding EVERY other feature, whether its MMS, video recording, cut/paste, etc, etc... they fell into two categories. #1.) Difficult to determine a decent solution given the UI or solution would take longer than launch to develop and test. #2.) This feature was crossed off the list of features intended for this device, and will likely show up in future devices, or not at all.
I strongly disagree with ANYONE who simply thinks Apple doesn't understand the market. That just seems foolish. If Apple wanted to, they could have developed the product for another 6 months, or even a year. Apple has ALWAYS been about "simplicity" and "minimalism" wherever possible. I was always angry that the desktop search in the Mac OS never accepted WILDCARDS. Now, however... there's almost no NEED for them using Spotlight and instantaneous feedback.
Not releasing the iPhone with diskmode and/or file browser annoyed me. Rumors that it will be FAR more full-featured and gorgeous than any file browser any phone has ever seen (with coverflow and Quicklook supoprt no less), is encouraging, and makes much more sense. Better to release something LATER than POORLY . This is a subjective statement, true... but I couldn't agree more. If the MMS support was tied in with a later rev supporting video recording... so be it. By the end of the year, we'll know one way or the other.
As I've said... people BUYING the iPhone, should by it for what it HAS and does well. NO ONE should by it for what they expect it will do. That said, I have high hopes that there is an update being worked on in parallel to the launch that simply couldn't be finished soon enough. Early rumors were that the phone would receive a firmware update on first use. We'll have to see what they cook up.
~ CB