so all the data on your iPhone is completely different from all the data on your iPad? i have 4 iOS devices. i would say that 90% of all the data on each device is redundant. get it?
yes, iCloud can be used as a backup service, but that's not the primary feature. if you use any other backup service, you realize you have to pay for it right? mozy and carbonate are about $60 per year. and this is for you desktop or laptop, not your mobile device. even dropbox charges $10 per month for if you use more than 2GB.
It doesn't matter if the data is the same or different if you're using it to do backups.
The point is - I can register all these devices on new accounts and get 5GB each. If I register them on the same account, I should get that same 5GB each. Why is there a penalty if you're purchasing multiple devices? I would think you would get rewarded. You actually get less than a new customer.