How many times has a word count being questioned? Well, it is not just a matter of what parser and settings have been used, but also the amount of considerations and exceptions in place. Here, these guys tried to explained it and they did a very good job while at it:

https://tradoshelp.wordpress.com/2011/06/20/word-count-differences-between-trados-studio-and-trados-2007

http://multifarious.filkin.com/2012/11/13/wordcount