Server emulators(what you define as a copied server) are often developed along the lines of the first IBM clones were, here is a good summary of how they came about: Clean room design
Basically, a way you can create code that copies the FUNCTIONALITY of a known system without copying the form in any manner. There can't be any accusation of copying the original work, since no one has access to the copeid servers code base :P Proven to be safe from copyright issues several times in court, even with Sony leading the charge against it.
Something like Diablo 2, or the new Simcity, which can play independently of the main server and only requires periodic connectivity to sync, are good examples of thick clients.
Also, while the loot tables exist in the client, they are there as a part of a resource that is published to both the client and the server; the client does not control loot generation, it merely has access to libraries which are published to both server and client(because its silly to build multiple libraries when you can push the same one to both server and client and just not utilize the extra stuff on the client). If you are bored, you can always verify this with something like Ollydbg and Wireshark.
Thick client - can work independent of main server for extended periods of time
Thin client - some logic work on the client, but requires constant connectivity to function
Dumb client - no logic local to client at all, all work done on server, often only handles screen draws or terminal access