Why sound a Dur scale better than a random collection of notes???

[Lazos]

Just to be clear, JJF, your reasoning that because of the nature of melodic minor having a raised sixth and seventh on the way up and those notes flattened on the way down points to the mutability of the scale. The same thing occurs in Turkish music in many many makamlar (not just the ones we in the West would call of a minor tonality). It occurs in makamlar that do not exhibit either tonality or both within the same compositions They call this ascending/descending attraction and is more related to properties of melodic modulation (modulating between makam) than any need to give "proper" voice leading to a singer.

This is what happened in what you call (somehow depreciatively?) western culture, before the advent of tonality. When composers used the modes, they changed form one mode to the other (that's where the term "modulation" comes from). The turkish "modes" (I think I can call them that), being probably inherited from the byzantine tradition, have similar behaviours.
Unfortunately, tonality leaded to a simplification of the modes, but tonality evolved, and in the XIX century (with Liszt, Wagner, Bruckner, Mahler, Max Reger, until Schoenberg and the second Vienese school) the tonality turned in "progressive tonality", reaching complete dissolution with Schoenberg.
Later (but almost at the same time), composers like Debussy, Ravel, Stravinsky, followed by Messiaen and others, returned to the modes, and (specially with Messiaen) expanded very much that universe. It's amazing how people keep talking about tonality as if the "westerners" (means US) didn't got way beyond that - we did, many, many years ago. Already.

I'm a fan of a lot of different music, so not being "depreciative" on purpose. You could call the Turkish makamlar "modes"; often each makam is a collection of "modes" or flavours (a tetrachord/pentachord from this or that scale played in particular fashions). The Byzantine tradition influenced the Ottoman tradition (and vice versa), but the Ottomans more directly inherited and established their own tradition from the Persian tradition.

[JumpingJackFlash]

I'm not confusing scale with key at all, though. Remember that key is a Western concept not necessarily present in other cultures.

So is our major scale.
(Although the notes that correspond to it may be present in other cultures, it definitely doesn't function as a major scale)