These two aspects are fundamentally different and not interlinked: You can have a tightly controlled single marketplace for apps built using Open Web technology which only run on one particular device, operating system or browser based on the distribution scheme of the market. On the other hand you can have a multitude of markets/stores for apps which are built to run on a single device/operating system. Both might be referred to as open - the first is open in the sense that it distributes apps which are built using open technologies (though the market is not open), the other provides choice on the store side, which is an open market - but distributes closed apps.
Obviously the most open approach is an open market (many stores) for apps built using open technology (no device/OS lock-in). This is what we are building at Mozilla at the moment.
So be careful when you talk about open - open doesn't always equal open...
[Photo Credit: wiccked on flickr]