ethereum running out? no worries! just create a new currency ethereum2, issue 100billion and use the blockchain to power more apps.
In fact you could just have several ethereum clones going at once.
It's true that something similar could be implemented any time (at a cost). However, the same can be said for Twitter or Facebook.
The analogy to oil is not very useful, it seems.
But I also see it as a a problem that Ethereum presumably doesn't have a huge user base yet.
Atm Bitcoin still seems the only safe bet for the long run.
Ie. how much will selling/buying a certain amount of the currency affect the market price. This is what defines money: high liquidity (market depth). Something cannot be money without this property. It might have the potential to become money, though. But without liquidity it is as much money as baseball cards and wine.
Those stats determine where most of the resources have been focused on. Each coins have their own agenda, goal, and different group of community backing it.
i suppose the idea is that it 'burns' ethereum to run an app on top of it, so I can see a scenario where ethereum becomes too expensive and businesses that use decide to move to a different fork that is less expensive.
I guess the oil analogy works then -- it gets too expensive and alternatives are found. However, its just a matter of forking the codebase and starting another one...kind of like stellar did with ripple.