"MMS messaging is available only on iPhone 3G or iPhone 3GS; fees may apply. MMS may not be available in all areas. MMS support from AT&T will be available in late summer."
Even if it's a technically justifiable and insurmountable one?
I don't think Peter said it was insurmountable, that's going a little far. He said they applied developer resources to other aspects of the OS that were more important to have finished/working at launch.
I'm pretty sure there will be an MMS update soon after release anyways.