I'm going to write a fairly long answer here, because "isn't this easy??" comes up a lot. Before I do, though, if you think what I'm about to describe *is* easy, then I'd like to point out that webdiplomacy is open source, and we welcome well-tested and well-written contributions. The github link is at the bottom of every page.
Firstly, usually code changes aren't actually as easy as one would expect - there's a difference between how easy something is to implement if we have to have it done RIGHT NOW, and how easy something is to implement if we want the code to still be clean and easy to maintain later.
Think of it like doing the dishes after dinner- sure, if I want to clear the table, it's easy to just put the dishes in the sink. But, if I keep doing that every time I want to use the table after dinner, over time the dishes stack up - and not only can I not clear the table, but I have a lot of work to do if I want to use the kitchen again (including cleaning dishes with dried-on mystery food).
Code is like that - getting something done now is easy, but getting something done in a clean way that isn't going to cause problems later down the track requires a bit more thought. WebDip is actually extremely well written - Kestas has put a lot of effort into the design, which means that maintaining the code and adding new features is a much nicer experience than it usually is with php projects (for those of you who don't know - although I've contributed most of the recent code updates, webDip is still 99.9% Kestas' work. And calling it a house of cards does a great disservice to all the hard work that he's put in). Sure, Kestas would probably be the first to tell you that the code isn't *all* clean, but as someone who's read a lot of his code, it is *generally* very clean. And even when it isn't, it's still easy to read.
In this case, the code change is (I think) actually pretty easy. I think the fix is probably two lines - one to remove the call to change the ownership of the supply centres from the current location in the adjudicator, and one to put it somewhere else (probably in the code that progresses the turn to the build phase).
I think those changes are probably all it takes. The key here is *probably*. We have nearly 2000 users currently playing in games - let's say I overlook something in making the change, and now supply centres don't change ownership correctly in some rare case (say, for example, when supply centres change hands but no-one has any builds - a bug that we could absolutely introduce - though I don't intend to).
We're not going to ruin a whole bunch of games just because I thought that the code was *probably* right after a fix. If we're changing the adjudicator, we're going to be very careful about testing it. As jbalcorn points out, this kind of dedication to testing is what's expected in software development. Unfortunately, webdip doesn't have any automated tests outside of the DATC, which means that we're relying on manual tests. And manual tests take time.
Even then, yes, it's not a *lot* of time. We're probably looking at an afternoon's work, max. However, webdip is a hobby project - no one is paid to work on it (and we plan to keep it that way). Everyone who works on the site does so in between work, life, and other hobbies. Working on the site includes things like new features (RR and the upcoming ability to add games you're not in to your home page), bug fixes, and borrowing features from our sister site, vDip (this includes the recent move previews and ability to mark press as unread). Finding four hours to fix and test a bug like this means that there are four hours not spent on other things. Adjudicator changes take more time because we're much more thorough about testing them.
Don't think that this isn't a priority, though - Hellenic Riot and the mod team kindly spent a few hours last night helping me set up some tests for this. We're working on getting this fixed, along with all the other improvements we have planned (including working on modernising the site). The next year should be an exciting time for webdip. But, don't expect this change tomorrow.
To see what we've been up to, we have a list of recent changes that you can see at http://webdiplomacy.net/recentchanges.php , and don't forget, we welcome code contributions in github pull requests. One of my goals for the year is to grow the dev team - please drop me a PM if you know how to use php/mysql/git and you're interested in helping out.