This happens in every game, though. Items that are rare and very desirable in launch get more and more common as the time passes. It is unavoidable unless the developers set a specific limit on the amount of those items (such as there can never be more than 1000 of them) or that they are impossible to create after a certain time limit, which leads to a fixed amount of the items as well.
To me the LUCK act like a gate around the legendary. All of the other mats just requires lots of time. So with RNG it becomes a question of "Do I want to actively go after legendary and waste a lot of money attempting the precursor? or Do I want to blow 300g on a precursor? That automatically cuts the amount of people that will have legendaries in the near future by a significant amount (what I mean is RNG act like a mental ro* to the majority of players), which helps to solidify their place as indeed legendary (admittedly arenanet could have use a different name than legendary since a lot of people seem to take the literal definition of the word "legendary").
With a recipe EVERYBODY will be able to make it which just makes legendary no more special than exotic , the essence of legendary is to limit the amount of people that have it, to make the owner standout (whether good or bad those are irrelevant). The other problem with having a set recipe, well it destroys the purpose of mystic forge which act as a item sink. As a result of the very random nature of the mystic forge, well it helps to reduce the rate money comes into the system (ofc this is only secondary).
Going back to my main point, having RNG reduces the rate of legendary weapons being introduced in the system which inturn helps solidify their presence as legendary.
Edited by Specialz, 17 October 2012 - 04:47 PM.