One reason altitude limits are placed on displays using CCFL backlights (and any laptop using them) is because of the high-voltage used. As designed, the power supply and cabling assume a certain amount of insulation provided by air. As the altitude increases and density decreases, so to does air's ability to insulate the high-voltage connections and cabling. The result can be arcing, which could damage the cabling, connections, and possibly the supply. (At 18,000', there's about 1/2 the pressure there is at sea level.)
And to reiterate: you cannot survive at 30,000' with just oxygen. It must be pressurized to make up for the low partial pressure at that altitude. In other words, you could breath 100% oxygen, but your body can't absorb it. it'll just give you some extra time before passing out, but can't sustain you continuously (for example, without any oxygen at 24,000', you have about four minutes).
The emergency masks that drop down on airlines aren't pressure masks; they provide enough supplemental oxygen to keep people from passing out during the time the aircraft is making it's emergency descent to 10,000' (and, it's not very long before it's low enough that pressurized oxygen is no longer needed).
