ok maybe you know ... who invented this term? : "provably fair" :\
You avoided addressing any of my points, as expected, but that's a reasonable question.
I don't know the answer.
The first time I came across the concept of provable fairness was on bitjack21:
As of 8/9/11 I have enabled the "crypto-proof" system on the website. This system is a mathematical PROOF that every hand you play at http://bitjack21.com is 100% completely honest. (Technical details at http://bitjack21.com/cryptoproof )
but as far as I know they never coined the term "provably fair". Is it the term or the concept you're asking about? If it's the concept then I think that's your answer: bitjack21 invented it as far as I can tell.
The concept became incredibly popular with the rise of SatoshiDice:
Bet options are available with up to 64,000x multiples and a house edge of only 1.9% (and bet results are mathematically provably fair).
That could be the first time the term was used, but I'm not sure.
The place that I first saw provably fair done well was at Bitzino, where they allow the player to specify a seed after publishing the server seed hash:
I am the creator of bitZino - a provably fair HTML5 bitcoin casino with a focus on ease of use and a slick UI.
I hope that answers your question.
Now can you tell me how it is possible for the house to cheat on a provably fair site without being caught?
only a truly isolated and spiteful mongoloid could conceive of
Wait. Are you Klye? He's the only person I've ever seen use that word.
no you don't have any idea yet fools like you throw this term around like its some kind of bitcoin gospel!!! rotff!!! 
A gospel is an account describing the life, death, and resurrection of Jesus of Nazareth. Whether you believe the account is a matter of faith. It's impossible to prove the content true or false.
That's nothing like provable fairness, which is a mathematical feature of a site. I guess you could argue that it requires faith to believe that it's almost impossible to find sha-256 collisions, but that's a stretch.
Basically people "throw around" provable fairness as a useful concept because it works, not because it's a story they like.