Think of it like solo mining. You don't get paid until the block is cracked open. Well that is what happens here, although on a larger scale. Hundreds of users are working on one block at a time, and the 50 coins are distributed to everyone once the block is done (and finished validating). You aren't paid for each individual share like with PPS.
So some times it will only take a few minutes (if the pool is lucky), using only a few thousand shares from everyone to crack the block open. So even though you may have only submitted lets say 20 shares, you will get a lot of BTC for it since it was solved fast. So you might get something like 0.2 BTC for that block if you were mining at 2GH/s. So getting paid 0.2BTC for 20 shares is incredible. However, sometimes the pool might be unlucky and solve a block after 16 hours. So you will still be paid 0.2 BTC for 16 hours worth of shares mining at 2GH/s (which is what... 30,000 shares maybe?).
So what is the difference between DGM and prop in the example you gave me?
In solo mining, you have an equal chance getting lucky or unlucky when solving a block. This makes its completely fair so in the long run your luck should be "50%".
Except their is a problem when you are collectively mining with others. This problem lies in the way how the coins get distributed to the miners depending on their work input.
So here is a summary:
PROP: If everyone was constantly mining without leaving the pool then this paypout system would be fair. In this case everyone would get paid for their share of work. The miners luck would vary from block to block, but it would follow the same exact concept as solo luck.
But lets say I only mine the prop pools when I get notified that they started working on a new block. So at this moment, lets say I go over their and I mine the fresh block only for an hour (this is lower than the average solve time). After this hour I then switch to a PPS pool. In this scenario, since I only mine at the beginning of the blocks on the prop pools I have a high chance of getting the high payout. Given that the the block is short. If the block is long, I still get a fair payment for my short amount of work submitted to the block. Now after this hour I go to a PPS pool. In the PPS pool the variance is swallowed by the pool operator.
In this case, I get a high chance to get overpaid on the prop pool. And then I get paid at 50% luck **minus the pool operator fee**. My extra profits come by ripping off the long term users of the prop pool.
PPS: In this situation I get paid at 50% luck, minus the fee since the mining operator has a chance to lose depending on the long run of the pools average luck.
Score Its a formula where beginning shares are not worth as much as the later shares. This throws off the pool hoopers since its the opposite on what happens on prop. In this case, miners gets paid less on lucky blocks, and gets paid more on long blocks. This is okay since it all balance outs just like solo, and hoppers trying get an unfair advantage are eliminated.
DGM From what you explained, its exactly the same as prop!!! Which has some serious flaws. What is the mechanism to deter hoppers?
EDIT: Went to the link. Explained everything.
DGM is nothing like prob. I cannot find any holes in the theory.