Batteries don't stop working suddenly.QUOTE]
An ipod with a non user replacable battery is not a concern as that is entertainment not productivity, the problem with non user replacable batteries on a laptop is that you are in no position to make the most convenient swap of "ooo look my new MBP battery just arrived in the mail, let me swap it out now and get it charged up"
IF you do happen to have a conveniently located Apple store then life is grand as you can probably book an evening or weekend appointment to have the replacement performed.
Unfortunately not everyone is blessed with a local/mildly convenient Apple store and will need to send the laptop in for replacement when that time arrives.
For a productivity device "consumable" items should be user replacable, on entertainment devices it is whatever is convenient for the manufacturer.