They wanted to leap-frog the competition, and they wanted to maintain the same proportions. It's pretty simple really.
Also, as they said on the gizmodo review, the individual pixels were virtually indistinguishable because it is such a high resolution on the same screen size. Apple really likes mystery.. haha
And yes this will do WONDERS for Safari. Viewing pages in landscape is going to be the most amazing mobile experience ever (besides iPad, but that's not exactly mobile in every sense).
OOH you know what would be cool! For the presentation, they should start with ..
Blah blah blah statistics blah blah blah revolutionized etc. etc. etc.
Now let's talk about the screen.
We've got the same 3.5" multi-touch display you all know and love, but with 2x the pixel density.
*shows a beautiful, high quality photo in photos app, zooms in, incredible detail*
*flips through several other beautiful, breathtaking photos, some taken at night, all very clear and high quality*
And all these photos were taken with the new camera."
DUN DUN DUNNNNN
That would be a goood little snippet. People would **** themselves if the camera is really capable, which I think it will be. The lens is 2x the size at LEAST, and it's probably 8 megapixel and 720p recording.