This would indicate it is auto-switching:

http://docs.info.apple.com/article.html?artnum=1306

which is also what appear on the case bottom of mine and JDW's:

Unless someone knows for sure, I'd like to open up my PSU and verify what's actually inside the enclosure, one of the only pics JDW didn't post!

Either way I doubt it'll be a major hindrance for you.