You're really not. People have been buying things from the Marketplace because it is Alpha and things have been made cheap purposefully so that people get to play around with it a bit. The only advantage the Marketplace gives you is that you can buy food and supplies, bags, and ammo. That's it. You can't buy weapons (apart from the baseball bat in Alpha so that people have a chance). The idea is to find what you need in the world.
I haven't played since Wednesday evening now, but my understanding is that you're only able to access the Global Inventory in the designated safe zones - which are presumable where the civilian populace will reside and hand out missions. This was implemented so as to stop people loot farming with no repercussions or threat; now what is in your inventory stays in your inventory until you use it, drop it, or make it to a safe zone and place it in your Global Inventory.
In my mind it makes perfect sense - it's no different to a Bank on WoW.