The buyers have lost their BTC, because Counterparty made a centralized decision to roll back the ledger, therefore asymmetrically alter the transactions which previously had occurred. This was done with full knowledge that the people who invested in XPC for the long or the short term would lose their BTC.
We didn't rollback anything. The only thing that we did was close a loophole in the parsing code that allowed for the misidentification of the source of a transaction.