I was trying to figure that part out too. This article begins to go through what's different.
So in other words, it's not really a stimulus. If you say you're going to give $1b to the Greeks but if they don't pay you back they're on the hook for $800m, you've actually only given them $200m.Unlike the U.S. version of QE, the European plan involves keeping most of the losses contained in the country where they’re incurred. (This is analogous to allowing the states encompassed by the Chicago Federal Reserve bank district to largely fend for themselves.)
When the ECB in March begins buying 60 billion euros' worth of securities from European institutions every month through September 2016, any financial losses that occur will be largely contained inside the countries where they happen. When ECB President Mario Draghi announced Europe’s QE on Thursday, he said the eurozone as a whole will absorb 20 percent of “risk sharing” while the rest will “not be subject to risk sharing.”
This means that if a bank investment goes bad in, say, Italy, 80 percent of the loss will stay in Italy. “There’s a serious issue about how this is going to work,” said Cecchetti. “I’m concerned that this will dilute the effect of QE.”