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?).

This is still how other PPS pools operate, and in fact all pools worldwide. Just instead of you being lucky or unlucky, you are always paid at a constant rate (PPS). So it's the pool operator that is making a fortune, or losing a fortune (depending on what the luck was behind the curtains), even though a pool is using the PPS method.

DGM saves the pool operator's (Inaba) butt because he's never really going to have to worry about going into debt for awhile when there is a bunch of unlucky blocks. So the pools that run PPS, their operators can have both good days, and bad ones.

tl;dr
DGM is like solo mining. You are paid once the block is opened, and shared with the whole pool. You aren't Payed Per Share.