Yeah, that's been a problem for a long time. The main reason I haven't fixed it is because I'm not sure what the future of the theme area is.
The main issue is that the Current Theme is only really needed when you have multiple physical themes. Now, it's been the focus to have only a single physical theme and everything else to be done with CSS.
This raises the question: is it something we're going to push forward with in the future or not? For the core, I think this is going to come down to the eventual fate of the wireless setup. Right now, we have the wireless skin, which essentially drops certain layout items from across the site. It's an improvement on the default for wireless, but not by a lot. I'm increasingly feeling like I'd rather have a full mobile theme that has its own templates (a la Dragooon's SMF4Mobile), which means bandwidth can really be trimmed for mobile users and that would be set up as a physical theme.
If it is a physical theme, we ensure that everything works - because right now, I really don't know how well any of it works, mostly because the skins system essentially has removed most of the need to care about it. On the other side, if we were to have a physical theme for mobile use, it could easily inherit skins for changing the colours and smaller layout items even on mobile, which seems pretty ideal to me.