About the Auto-Updating Patch, I've heard a few people I know that the patch didn't work for them.
Otherwise, my concern is if the translations are truly accurate. In particular, the endings. Since if I recall, the auto-update patch translates 打ち出の小槌 as "Uchide's Mallet" in the ending (Reimu A's to be specific), while translating it as "Lucky Mallet" in Reimu A's Scenario.
It also does this with 小人 , translating it as "Inchling" in the Scenarios, and as "Kobito" in the Endings.
I don't know, but seeing translations in the game flipping back and forth kind of gives the impression that the translations were quickly hammered out without any concern for it's accuracy or that no one checks the translations over to make sure that they are as accurate as possible.
Unlike common misconception (I think?), The auto-updating patch does not rely on "The Wiki", as in
http://en.touhouwiki.net , for it's translations. While I don't know too much about the integrity of en.touhouwiki.net, from my knowledge, the translations here seem to be refined until they are as accurate as they can possibly be. The auto-updating patch relies on it's own wiki, which does not use translations from en.touhouwiki.net
Edit: From further exploration, it seems that the past games do refer to en.touhouwiki.net 's translations. So I guess the real question is, why doesn't DDC?