I say tomatoe...
Can you read multiple e-mail messages simultaneously?

You are spot on in that you aren't allowed to throw multiple instances of mail into the scheduler. But I don't think that is a negative and CAN'T is different from WON'T.
On a tablet device I wouldn't want a full footprint of the same app instances taking up primary memory. Nor would I want a battery powered device wasting cycles running e-mail in the background. That is why I have a PC hooked to AC!
Android takes a desktop OS task scheduler and shoehorns it onto a radically different form factor. It's not that iOS can't do that kind of multitasking, it just doesn't make good sense for the form factor. That may be frustrating to users especially when you are used to a desktop OS, but I'll trade intelligent resource management (including extended run time) over not having to save to drafts to refer to another message any day.
So yes, iOS really does multitask, and in a manner that is well suited to the form factor e.g., I really can listen to my music app in the background while composing an e-mail message.