That's not necessarily true. I don't know if it is still true, but I know in the past Apple limited the max brightness on the iPhone likely because of battery concerns. Apple simply decided that nobody needed the screen to be on full brightness and didn't want to see battery life issues as a result of people needlessly maxing out the brightness. But you could download flashlight apps from Cydia that bypassed iOS's brightness limit and get an even brighter screen.
Is the same true for the speakers? I don't have a clue, but it is possible that Apple intentionally limits the max volume output because the quality of the sound isn't as good when it's up at its max volume. And if that were the case, a software tweak really could "fix it". I'm not saying it is, just saying that theoretically a software tweak could be all that is necessary.