And I dare an engineer to come up with an igloo unless he went to the University of the north pole and lived with the natives in 1800.
But that's my point, the Engineers came from those Pioneers who developed methods to perfect the structures and then document the process so that other could learn and develop advanced designs. The Inuit in igloo design were the Engineers of their time.
Too many other things to really respond to, but people are human and humans make mistakes. Well all the ones I know of do, me included. It is somewhat facetious to cite failed structures and designs. To be balanced, if you are going to cite failures, one should always cite successes and I am sure that ratio would be very unbalanced values. Something like 100,000,000 : 1, success to failure of course.
There are often many more issues involved beyond the control of the Design Engineer and the design they are developing. Budgetary, Legal, Urgency of Need, Deadlines and of course the worst cause of shortened development times, Investors. That list too could go on almost forever.
OK, so the placement of the gas tank on two models of motor vehicles was not the best option, but probably for budgetary reasons they were forced to make the most of what they had to work with. Rent the movie "Class Action (1991)" with Gene Hackman, risk assessment is real and in our ever day lives.
OK, the toilet: Well, I assume you meant "how the bowl fills" and not "the tank fills." Wasting a few flushes and watching stuff closely, it appears the holes at the top ring of the bowl reduce the flow sufficiently to store enough water for filling the bowl. There is a hole at the front-base of the bowl about 1-1/4" diameter and a solid jet of water scoots the poop'n'paper out in the first few seconds of the flush.
There is a small amount of clear flow back from the "S" bend as the water level stabilizes about an inch deep. The top ring holes continue to to allow water to drain into the bowl to refill to the stain line. It all looks and works perfectly -- by design -- dare I say??? LOL

It seems to be the model of efficiency and not to get too gross, there have been some pretty gnarly volumes to dispose of at times and we have never yet had to flush twice. Well, I may white-lie there, I recall trying to dispose of a black-Widow spider that hung on for four full flushes before making the big swim to the septic tank. She couldn't get out and I was not going in after her. Ahh, country living and things that crawl in the house.
I suspect the top-ring holes have been precisely sized to "well" sufficient water in the top ring, while the Jet-hole takes care of scooting the P'n'P.
Oh, and as a parting shot, the hanging walkway was not designed to carry the number of people that was on it. The permit and rating for it (as with Elevators etc) was clearly marked at both ends, there was almost four times that number of people -- AND -- they all rushed to one side to see a show going on below. Anything will fail when stressed beyond reasonable design limits. If one can get seventeen people into a Volkswagen beetle, then I am certain you could squeeze sixty people into an elevator licensed to carry ten.
http://www.youtube.com/watch?v=9O-u9SlnhOo