Right, I agree. I think it is just lazy from the manufacturers to not wire the shift levers to the derailleurs. It should have a similar weight because you need additional cables but can get rid of the batteries within the shifters. Your main battery will last about 50% longer too. The only downside is the added work to wire them when assembling the bike. After that you can pretty much forget about the wires though.

Once I had the proper tool, I wired mine. They are all internal so I don't think I'll need to replace during the lifetime of the bike.