Closed source OSes are such a bane.
It's actually not. As a user I'd expect the device to wake up and still have the same IP address via a continuation of the lease.
Yes, the correct way would be a longer lived DHCP lease, but el-cheapo ISP routers often lock down such settings.
Most users don't know what IP addresses even are, let alone care what theirs is. I don't think Apple is (or should be) optimizing for you.