Well, i don't think including a floppy drive cost apple, or any other manufacturers much money. considering during the last legs of the life of 3.5 inch drives, they were costing around $20 to consumers, imagine what they cost wholesale? and in bulk?
It was more of "This technology is useless, it only allows for 1.44Mb of data, and the CD is much better suited to modern day use."
So, the same applies to MMS v Email, MMS doesn't allow for modern day high resolution images, it's not reliable in terms of how much data it will or will not allow (each network sets there own limits on how much data they'll accept). And as such Apple just thought.. "Lets not bother adding complexity to our user interface for essentially a dead technology, and instead lets focus on kicking ass at using email!"
At the end of the day, the reason the iPhone is good, is cause it's easy to use, and has a limited feature set. limited in sensible ways too, that help push technology forward, and not pander to old deprecated technologies such as MMS.