I thought that one never uses an "s", just an apostrophe, when making a name that ends in "s". I swear I put that reason in the summary box when I changed it back but it didn't save. -Shorty1982 20:20, August 31, 2011 (UTC)

Just did some Googling and it looks like both are technically correct. -Shorty1982 20:24, August 31, 2011 (UTC)
It has been conventioned around the wiki that an apostrophe alone is only to be used to form the possessive case of plural nouns ending in "s" (i.e. "Potters' cat"). The possessive case of singular nouns (including those ending in "s") is formed by adding "apostrophe + s" (i.e. "Roger Davies's girlfriend"). --  Seth Cooper  owl post! 20:34, August 31, 2011 (UTC)