More precisely everyone got the same currency but didn't have to actually live by the stability pact. The politics of Euro membership were more important than the reality. Greece should never have been allowed to join, France and German routinely ignored the Stability and Growth pact.

The problem with DB is that Germany cannot let it fail because it underwrites its export economy, plus it would be a national humiliation. However bailing it out after imposing austerity on the PIGS, especially Greece would pour fuel on the fire of anti-German sentiment in the EU.