Second of all, it seems that many Bitcoiners complain when aspects of Bitcoinland become "centralized"... and yet here we have MPEx as a competing platform to GLBSE and people come out and complain that I haven't listed on the "main" platform.
Bitcoin benefits when all of the buyers and sellers can participate in the SAME MARKET. Unfortunately current technology means that we need a centralized place to buy and sell securities.
The real solution to decentralizing the equities market is not to have several isolated and competing exchanges but developing technical solutions to federate equities and create a single market with competing service providers.
I am currently of the opinion that the 20 btc entry fee on mpex actually further's this cause (so long as there are valuable listings on mpex).
The exchange has a high barrier to entry allowing for the proliferation of many brokerages (which themselves should offer services for all the exchanges out there ] I know of mpex, glbse, and icbit at least [)
that way, we have a central market by all exchanges being combined, loose this conflict of the exchange also being the broker, and gain lots more competition (which i think is good for the community).