This isn't new - it's probably Wikipedia's best kept secret though. It first got saved to del.icio.us in November 2006: http://del.icio.us/url/08d335d4c1d2f491cc70e1bf61e5d880

What format do they use? It looks like neither SOAP nor XML-RPC. It looks more like some home-brew XML-dialect.

Are they reinventing the wheel, and if so, why?

They're PHP programmers. It's a well kept secret, but PHP actually stands for "reinvent the wheel thousands of times because I don't know any better".

But hey, at least they don't have to install CPAN modules! That's hard! </sarcasm>

It is somewhat ironic that you said that seeing as CPAN is a whole collection of wheel reinventions...

You can also get the MySQL dumps (and have been able to for awhile):

http://download.wikimedia.org/enwiki/latest/

http://en.wikipedia.org/wiki/Wikipedia:Database_download

Wikipedia bots (ex. http://en.wikipedia.org/wiki/User:ClueBot) have been using this for a while (at least a year).

It's still a work in progress I think. It was hard to find for me too, when I built http://www.wikirandom.org