I don't think they hated each other as much as advertised. After the match if you look closely you can see Mosconi wink at Fats before they shake hands. They hated each other the way pro wrestlers hate each other. If people think it's a grudge match there is more interest.
Even though he was full of it most of the time it's hard not to like Fats. In this video at the 15 minute mark you can see Mosconi telling some kids in the audience to stop distracting him. You would never see Fats do that.
http://talk.cuetable.com/showthread.php?t=1070
Mosconi was a perfectionist who had a temper. He swore a lot during his matches. And he resented that in many places, Fats was more well known than he was. Fats was more playful and funny, knowing that the crowd ate that up AND that it got under Willie's thin skin.
Willie was a 15 time World 14.1 champion and he considered Fatty a wanna-be who's claim to fame was self-promotion.
If you're interested in a real in depth look at their relationship, get R.A. Dyer's book "The Hustler and the Champ". Anything he puts out is top quality material, and this book is no exception.
Here's a link with some good reading....http://www.billiardsdigest.com/new_untold_stories/