It's a parctice that dates back to 2006 when the API was first written, and frankly isn't covered by the coding conventions. Same thing with the docblocks, they're all copypasted with some bits changed and don't even make sense if you look at them in the genereated code docs.
I don't feel that any of us depend on this anymore (get a better IDE), so in the inerest of consistancy it's time we said goodbye to it.
"I wouldn't object to stylizing the API code to bring it in line with
the rest of MW on principle, but I'm not gonna bother myself." --Roan
<http://www.mediawiki.org/wiki/Special:Code/MediaWiki/60657#c5108>
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* Move export/exportnowrap handling code out of the if(count($pages)) branch
* Add an error fallback to ApiFormatRaw (exportnowrap uses the XML formatter for errors), since Raw doesn't know how to format errors
* Accessed through the export and exportnowrap parameters added to action=query
* To facilitate &exportnowrap, add ApiFormatRaw, a formatter that just spits out its input without any formatting (not accessible through &format= of course)
* Fix up the action=query description message to reflect the deprecation of query.php
