Alexa has never claimed to implement the NOARCHIVE directive, they honor robots.txt and always have.
Alexa does not wish to crawl anything you want to remain private. All you have to do is tell us. How? By using a simple robots.txt file. Robots.txt files are the most widely used standard on the Web for telling crawlers where they should and should not go on your site. All major crawlers respect these robots.txt files, including those from Google, MSN, Yahoo!, etc.. There is extensive information about how to create a robots.txt file on our site at Webmasters Help page.
If you don't have access to robots.txt, such as a Blogger site, just write to them:
Here are directions on how to automatically exclude your site. If you cannot place the robots.txt file, opt not to, or have further questions, email us at info at archive dot org.
I wrote to them once for just such a reason, they took the data out, not a problem.