MPex -> Lost most of its trading volume (stocks) -> going down
Still more trade than the sum of all others, for one.
The fact that it won't list bullshit "assets" (such as the Asciminer passthroughs) isn't really a valid objection. GLBSE listed Pirate and that was the end of it, even if the entire mess allowed it to climb to something like 1/3 of MPEx' volume for a few months back in 2012. Take the am-pt volume away and MPEx has a solid 90% of all Bitcoin financials.
There is of course the issue that poor people can't get in directly (and if you discount the MPEx pt's out of the remainder of the above there's really very little left). This readily results in those same poor people misrepresenting the reality of the matter into more palatable terms, such as the quoted. This attempted misrepresentation has been going on for about two years now, with no visible deleterious effects for MPEx (even if the names that keep pushing it keep changing, so it'd stand to reason that they slowly get fleeced and disappear, only to be replaced by new, and equally clueless, "playas").
As explained back in January
It's a simple point of competition for finite resources. This is not quite as visible in fiat, because in fiat bs gov'ts can create and do create fake money to prop up wasteful/pointless paraeconomic ventures run by the "right people", which is just another way of saying "popular" (which is, of course, the wrong game to play if you aim for prosperity).
In BTC however, where resources are absolutely finite, there will only be so much BTC available for investment at any given time. This BTC will be allocated to the available investments somehow. Part of it will be allocated by idiots, on paraeconomic criteria like "we don't like MPEx". Part of it will be allocated economically. As time goes on the share available to the idiots to allocate as they see fit dwindles, and the share available to the rational players increases. Since human behavior is reinforced by success and (usually, except in the case of a really limited pile of hardcore idiots) discouraged by failure, the flow is even faster as individual people realize they are being part of the idiot group and jump ship.
Soon enough the situation reaches equilibrium, which is pretty much where we're at. In short, the beauty of economy is that it works.
None of this is to mean MPEx is perfect, by any means. That's not the point at all. It just means MPEx is the standard, and because stock exchanges are fundamentally a convergent, naturally standardizing market it also means the accretion trend will continue, exactly in the same way and fundamentally for the same reasons Bitcoin grows against fiat currencies.
It's by now impractical for any serious company contemplating being listed in BTC to forego the significant capital available on MPEx in order to favor a different venue (in fact, the cost of doing so can be calculated on the basis of the volume difference, and is in any case significant) for a variety of reasons, and certainly such an attempt would imply the modification of said company to include "being an exchange", which requires rare and valuable skills (programming notably NOT being one of them) and other human capital. Such an effort necessarily spells a movement away from said corp's core mission, whatever it may be (*).
A willingness to move away from the core mission, a cavalier attitude towards incurring costs and foregoing benefits all work together to paint a very unflattering picture in the eye of the discerning investor (If these people have any confidence in their business, why are they working on moving away from it to do something else? If they have the capital to pursue reinventing the wheel, why do they need my investment? If they're not interested in cashing in now why should I expect they ever will get my shares dividends?) and rapidly the convergence effects become very strong indeed.
In short: if you're a noob with no clue you have no chance making it on MPEx. If you don't want to sign a contract and in general don't plan on being on the level you have no chance making it on MPEx. If you plan on running some nonsense a la HYIP you have no chance making it on MPEx.
If on the other hand you have a legitimate business you have no chance making it outside of MPEx. This is a point of fact, not a point of argument: there have been bet sites coming and going for about two years. Once one listed on MPEx that was the end of that market, BitBet now dominates it. Same with dice games, same with everything else: kids can play around and pretend they're doing things until the adult exchange lists some adults. After that it's nighty night Gracie.
Nothing wrong with this, either.