Aren't all electronic stock exchanges matched trade ?
Sorry, to clarify the bid/ask are not set by market makers on GXG.
As far as I'm aware they're not set by MM on any exchange. The MM's perform the actual trade on behalf of the buyer and seller and they also step in if there are no parties on either side.
For example, I can set a price right now a on thinly traded stock and see that price direct in the market. I could do that on anything, eg apple.
Not sure what you mean by the 'The MM's perform the actual trade on behalf of the buyer and seller' - that's the job of the exchange (are you thinking of the NYSE's system or something?). As far as a lot of exchanges go being a market maker is just a vanity/PR exercise - they're obliged to provide a two way quote for x% of the time etc... but they don't necessarily have any advantage over a non market maker.
There are however quote driven markets where prices are actually set by market makers - this is where they actually fulfill their job description of making a market by providing two way prices for other participants to trade against - generally this is used for less liquid stocks (for example LSE's SEAQ) - obviously you need two or more market makers... but aside from the market makers there is no means for others to enter limit orders directly into the order book - you have to cross the bid/offer if you want to execute a trade. (There are fairly obvious criticism of this approach but its still used for the smaller AIM stocks AFAIK)