Macbook with Thunderbolt setup

i am very interested in the Thunderbolt display, i currently have a mbp and would love to use the thunderbolt as a dock to charge and do work on, what i dont understand is, why or how does the thunderbolt cable come into play? if the thunderbolt display, is simply "displaying" or "mirroring" then why do you need the thunderbolt cable? you are not transfering data and the thunderbolt display does not have a drive to store anything on? i am trying to really figure out what makes a difference between a 300$ LG display or a Thundrbolt display? dont get me wrong i have two macbooks and imac got the iph5 on septemeber 21, every accesory apple sells i pretty much own so this is not criticizing apple in any way i just want to know 1. what is the benefit of this display over similar 27 inch displays? 2. can you attach an external hardrive to this display without having to disconnect it everytime you disconnect your mbp(read that on the forum)? 3. can you mirror it using airplay since your not transferring any data, unless you were keeping an external harddrive attached to it? 4. and what is the difference between the cinema display and thunderbolt display?