Dragon wings. They are curious constructs, are they not?
I once estimated that a mid-sized dragon weighing the same as a large bull elephant, about six tons, would be largely similar in size (length, wing span) and weigh to Chance Vought F4U Corsair. However, a dragon typically has slightly larger wing area, and therefore lower wing loading which reduces stall speed, but nevertheless I would estimate that in order to maintain altitude, the airspeed velocity of an unladen dragon must stay above 60 knots, or about 110 km/h. The portrayal of high dragons in flight actually fit this estimation fairly well; they are going pretty fast.
Of course, this also means that the dragon wings must have structural strength comparable to medium sized aircraft's wings, which is quite impressive from bone and
especially muscles and tendons. Of course, this isn't an impossible feat in locked flight configuration, and I suspect that like many species of birds, dragons also can lock their wings for glide, but for the dragons to be able to flap their wings, truly their muscles must be comparable to hydraulic pistons and tendons to thick steel cables. For the dragons to be able to control their descent in a stall, withstand the impact on landing, and even produce enough lift to hover is truly impressive from an engineering point of view - these things must have some pretty intelligent designers behind them!
Since dragons like birds produce both thrust and lift with their wings, the requirements on their bone structure, flight muscles and tendons are sky high, pardon the pun. For the sake of comparison, the heaviest flying birds are around 20 kg in size. If we were to grow this bird's size until it reached the dragon grade weight of six metric tons, it's muscle and tendon cross-section area would only increase up to 44 times, while it's weight increase would be 300-fold. That means, in order to produce and withstand the required forces for comparable operation, the muscles must be about seven times as dense, and tendons and bones made of seven times as durable material as the original bird's muscles, tendons and bones.*
So, estimated bone strength of a bull elephant sized dragon would be about seven to ten times that of bird bone, and similarly it's muscle density and tendon durability would have similar quantities.
Of course, a bull elephant sized dragon is not exactly large. But the problem with LARGE dragons is that they usually are proportionally scaled-up models of the smaller, somewhat sensible dragons. Which means that their stall speed would be comparable to a large airliner rather than a WW2 fighter airplane, and no amount of muscles could possible move those flappers of wings effectively enough to produce the thrust required to maintain such airspeed velocity, nevermind hovering or taking off from a standing start. Truly, some powerful magicks are required for these creatures to function.
This excercise should be sufficient to make you comprehend why materials such as dragon bone are so sought after for weapons use. I doubt even nanocarbon tube constructs would have better strength or durability.
In fact it might be possible to build a space elevator out of high dragon tendon, if it were possible to aquire a long enough piece.
*Of course, since it's wing area would also only go up to about 44 times the original, it would mean it would also need to fly about seven times faster than it's original-sized bird counterpart... it would also need to land seven times faster, and I shudder to think of the logistics of providing it enough food to power those turbocharged muscles. Not only would it require 300 times the amount of food as it's normally weighted counterpart, but the increased muscle power means its metabolism would be boosted up to about 7-10 times as high as the original bird's, bringing the required amount of energy content to about 2000 times that of the original bird.
And remember, this creature we're talking about here is comparable to only a very small, elephant-sized dragon.
This is a very good reason as to why dragons are typically very, very hostile to anything they come across. They are undoubtedly plagued by constant hunger and forced to use their magic constantly in order to sustain themselves. It also explains why dragons - especially large ones - tend to hoard magical loot and sleep on top of it most of the time.
IT ALL MAKES PERFECT SENSE! 
