There is some speculation that the AR2-3 may not be the engine used in current flights (see other replies to you post).

However, the AR2-3 is human rated. The X-37 is nominally unmanned, but hey the missions are classified, and because Halo Orbital Drop Shock Troopers. Of course some of the alternative engines you mentioned have been used on stages of previous manned flights and are thus presumably man-rated as well.

I did some Binging on the AR2-3 and found a NASA/Rocketdyne/OSC presentation that looks to be drafted around 2000.

Here that seem to make the case high test peroxide (HTP) technologies are the way of the future for upper stage propulsion:

Of course the Shuttle aspect is no longer a factor, but the other factors still seem to be in play.

Further into the paper, the USFE 10k peroxide motor is mentioned as a project to develop new HTP technologies. These technologies would be used for future HTP-based upper stages. They even have a goal of over 100 uses of an engine before it has to be removed for overhaul. Is that a lot in the world of rockets? As this paper was drafted around 2000 I would guess that the X-37 is using something a bit different that the bog-standard AR2-3 or has moved away from HTP technologies altogether.

Now to say that rocket science has moved away from HTP is not quite true. I don't think there are any big HTP engines used in lower stages. However, the Bloodhound SSC is using a HTP hybrid motor they are designing.

There is also research in to using HTP as a monopropellant for thrusters using a catalytic bed. I suppose the advantage here is that you have HTP as your oxidizer for an upper stage and then it can be used for maneuvering once on orbit. Similar, as you mentioned, to UDMH.

Take a look at the Introduction from the ESA paper referenced above. They cite several reasons why HTP is desirable and advantageous. Cost and safety being paramount. They also mention that Soyuz has been using HTP in its maneuvering systems for over 40 years. I think that HTP safety concerns have been effectively mitigated from the "explode because you looked at it funny" era.

As for performance it seems that HTP is as good as some other technologies, but it's no dog either and it seems to be a good fit for the X-37 or other small stages. Quote from the ESA paper:

It seems that HTP has many uses and rocket science has not moved away from HTP, indeed, it is being actively researched. It may or may not be used on the X-37 right now. It may or may be used on the X-37 in the future. With further attention to cost, safety, and, increasingly, environmental impact, HTP seems to be coming for you...

The show was probably about the Okavango River which empties into the Okavango Delta in Botswana.

You're right, none of the water makes it to any sea or ocean. Some of it simply evaporates. However, the majority of the water allows for a thriving ecosystem to exist in an otherwise arid region.

Include this into your analogy as you see fit.

I tried compiling "Hello World" using GCC 4.4.3 and then building it again five minutes later. The executables were binary identical. Is what you said only for non-trivial cases such as "Hello World"?