Merged mined coins such as IXCoin reflect the true cost - the horrendous cost- of Proof of Work in their market cap.
A lot of coins prefer to do without a secure blockchain, basically selling people a bunch of insecure garbage - refusing to implement merged mining because by leaving their coin insecure their market cap can pretend that securing a chain doesn't cost a fortune. However they achieve that pretense by not actually securing their chain.
Basically they are aimed at miners not at users nor investors. Speculators seem to like them too thoguh because speculators like moving along with the miners to new coins every day leaving the fools who fell for the previous days' scamcoins holding bags.
Basically the miners are trying to get paid without doing the work: they want the pay but have no intention nor desire to actually do the work of securing a blockchain, so they just do a constant bait-and-switch, making a coin look like it has miners, while cloning another con to switch to leaving idiots who bought their stupid scamcoin stuck holding the bag, while their tame "speculators" follow them on to the next bait-and-switch ponzi scam.
They don't want to support merged mining so their chain can maybe actually have some chance of becoming secure because merged mining tends to lower the market cap, as it should since it tends to cause the massive cost of Proof of Work to actually be reflected (priced-in) in the market cap. To an extent the change in market cap (between not implementing merged mining and implementing merged mining) is a direct reflection of the real cost of securing a blockchain with Proof of Work. SCamcoins prefer to inflate their market cap by not securing the coin so that the market cap does not reflect the cost of securing the coin, and of course they try to pretend the chain is not secure since they also hope the fools they suck into their bait and switch ponzi coin schemes don't realise the garbage they are buying is utterly insecure.
Coins like IXCoin already reflect that cost, and share it with a whole family of merged mined coins, so they all have much more honest market caps than the scamcoins; when they raise their market cap they probably do so in a far more "real" way than when the scamcoins do.
-MarkM-
You're right about merged mining being the ultimate goal for many of the long lived PoW cryptos, but I'm not sure it's a good idea to be pushing other coins to do this now. MM is the key edge iXcoin has over other more popular coins. I assume at some point someone will start a systematic purging of crap coins by using 51% attacks. When that occurs iXcoin should be in a good position to resist, but even very popular coins may not be able to hold up. So why give them forewarning if they aren't smart enough to figure that out for themselves. iXcoin needs time to catch up on marketing itself, whereas most new coins go straight to pumping. It's not a bad strategy because the pumped coins, if they are in it for the long haul, have the cash to pay for securing the block chain (MM) later. iXcoin has taken the path of securing first at the expense of its coin price. So it is slow to upgrade features and therefore vulnerable in the fast moving crypto market until its popularity rises.