I'm sure the coding here is complicated (anybody remember how buggy the ships used to be? In the early days of the game, there was probably a 50/50 shot that you would end up out in the middle of the water, having to swim back to shore on your own), but clearly this is a feature players want and Blizzard wants to implement, so why not just buckle down and fix it? Why keep pushing it back farther and farther? Give a programmer a clean room, a fast computer (or two), a case of Mountain Dew, and let him go to town until vendors are sitting on the boats.
It's probably not that simple, of course. There are probably a lot of issues with the code, and of course, programmers have lives, too-- even with Mountain Dew. But developers are always saying things like "would you rather us work on your crazy idea, or on something people actually want?" And this is something people actually want-- why not just get it done?