1- Unlocked phones are more expensive simply because locked phones are subsidised by the operator, that is, they reduce the cost in the hope that they will make back the money you spend by your ongoing purchase of their services.
Originally Posted by ericlambert
2- YES you will still get software updates for the device, but these will still be subject to operator approval (i.e. for devices with a Rogers firmware, Rogers have to give approval for the udpate). This is much, much faster on Windows Phone than Android, but there can still be delays. You should still receive the updates however.