...about why the ATC hasen't improved much.

http://www.fsinsider.com/Community/Developers-Corner/Assembled+Voices+Making+ATC...

Several things are covered:

• Voice talent
• Naturistic Sounds - including voice inflections and how it affects how the atc sounds in the sim
• Editing the Audio
• File Management

One interesting note is pointed out early in the article. Take ten different voice. Then have each voice cover over 45,000 words while each word has it's own sound file. That's 450,000 *.wav files. Even if each file is 10kb in weight, that's 4,500,000kb worth of data. Don't forget that each DVD has to make room for the scenery and other things. So having more voices as default would've required a third DVD for installation or a sacrifice of other critical files.

This explains very well why we were given a voice SDK to begin with.