Poloniex is a small exchange, yet seems to be overseeing 100 BTCs a day in trade. Bittrex gets about 10% of that, and I guess these two are the largest?
DRK is traded everywhere, so less chance for price fixing.
Cryptsy is too lazy to implement it.
They do just bitcoin clones they can add with 1 click, took them months to add NXT after other exchanges had it already.
It has a reason Poloniex is the only exchange where Mastercoin and co are traded.
Well its on Mintpal, Bter too.
DRK is on Cryptsy and Bitfinex additionally - is that everywhere?
DRK is on many exchanges, which you can find if you can be bothered. DRK is like Doge was, it got added by default for the numerous new exchanges that have appeared over the last 6 months.
Cryptsy does lots of X-Coins, not sure if any are cryptonote or whatever.
Cryptsy is not lazy, it is greedy and conceited. It will add XMR unless there is an issue.