I have sent about once a month or two request to many exchanges and answer have been same last one year about like "we will look and are really interested about this coin and will maybe add it later..."
Same time there is like Cryptsy what have taking every cat, moon, weed and car coins for trading. Why not XCP?
The simple answer is that the Counterparty software client is different to everything else. Whereas 99% of shitcoins' software are near identical to Bitcoin's. So it is a little bit more tricky to set Counterparty up on an exchange. Though, I find it difficult to understand why Kraken (they best exchange imo) saw fit to add Ethereum which is similarly different and they have not added Counterparty yet.
Last I heard it takes them $50k+ to fully security vet a potential currency. (Some Kraken representatives told me this... cannot vouch for the accuracy.) But basically it's a cost intensive and extremely long process. We will have to wait for Counterparty volume to go up, in order to be considered by Kraken.