Well, they didn't really break the design, it's more like a different design. With BitShares, bitUSD is only created when people lock up BitShares to create it on margin. SBD is a different mechanism. It still has the convert function which is similar to the settlement option in BitShares, but in many ways it's different. It's also debt, like bitUSD, but it's a debt against the network, not with those individuals who created it via margin.
I'd love to have a true pegged asset around here. Maybe with the introduction of Smart Media Tokens, we can have something like that in the future.