Word count??

I don't understand word counts. I really don't. I am in the middle of editing my Robert story and decided to check my word count in Pages. My words total 57,039.

Now on an episode of I Should Be Writing I recently listened to, Mur stated that your word count that is presented to editors / publishers should be an average but that is good because it's more words than actual words. You should format to Courier 12. Then take your number of pages times 250 and that is your word count. When I do this, it works in reverse for me and I don't know why. When using this format, I have 158 pages (up from 122) and that times 250 totals 39,500.

Somewhere in here, I have lost 17,539 words. Can anyone explain this???