To be fair, Windows Server 2008 is just as simple. Also, prior to this change, Apple Airports would, and still might, erase an IP/MAC address once the computer has been inactive for 10-15 minutes whereas even vanilla Linksys firmware keeps that information in the routing table until the DHCP lease expires, or permanently if you use DHCP reservation.
Again, without direct support from Windows, functionality like this is going to be difficult to program into the router. The router won’t automatically know if the computer is sleeping or shut down and the only way for it to be able to tell the difference is by sending a magic packet and seeing if the computer wakes up, obviously not what you want. The only real alternative to direct OS support is to tell the router to always assume that your computer is sleeping and has X services available, again not really ideal because a powered down computer will still have its services advertised to the network.