They are creeping in that direction though. Delta purchased their own refinery in 2012:

http://www.reuters.com/article/us-delta-jetfuel-exclusive-id...

Given that, "there is a deep, liquid market for jet fuel," is having Emirates airline and Emirates National Oil Company under the same umbrella poor strategy?

You're also omitting the fact/point that the energy industry is evolving very quickly and that calls in to question the established markets. Energy over-supply in general creates opportunities for disruption and new business models.

Yes. The only reason it exists this way is because they're both owned by the corrupt government/monarchy of Dubai.

Keep in mind that under the same umbrella you also have everything from banks to a cement company to hotels to a mineral water company. This isn't a coherent business strategy, it's just what happens when a single family rules over an entire economy and basically owns everything.

You could equally argue that is exists that way because they need to deploy extremely large amounts of capital. So, an infrastructure company in a region that is going through phenomenal, albeit temporary growth, makes a lot of sense. Once that growth levels off they could transition to higher-tech endeavors.