Geez you two, it's a patrial measure, and one lauded at the time it was implemented as well.
The second chat log window was added to tide us over until they resolve problems with the UI that prevent the log windows having more than two tabs at a time. Back at launch, we only had the one, and two tabs only within it. Supposedly more tabs per log window is another feature of the UI overhaul they're working on.
Besides, it's optional, and I get a damn lot of use out of it myself. 'Let's me keep track of LS and /Say or /Party without having to keep faffing about with tabs or pick them out from each other in a single frame. I'd be pretty annoyed if they pull the second window when they fix the problem that necessitated implementing it in the first place, frankly, even if I do look forward to having more than two tabs in each of them.