I get the sense that AppleScript is more respected than AutoIt. I think that it's something you can put on your resume whereas AutoIt is not. Is that the case? Why is that? With AutoIt you can automate just about anything. Is that the case with AppleScript? With AppleScript can you make it detect arbitrary images on the screen like images in a web page?
Both languages serve very different purposes. They both started out with similar goals in mind, but evolved differently over the years.
AutoIt has adapted GUIs and has become more of a general purpose scripting language. It also has a large following of developers that all contribute to the functionality of the language. Applescript focuses mostly on what AutoIt was originally designed for, automation.
What really separates them on this focus is that AutoIt interacts based on commands and properties of Windows, where as Applescript interacts based on commands and properties of the application it is automating. Applescript is more similar to OOP, where as AutoIt is a traditional procedural language.
Why one is more popular than the other? that is a difficult question. I actually learned about AutoIt years before I knew anything about Applescript, but that is because I worked primarily on Windows and Linux machines and rarely on Macs. It really isn't a fair comparison to say one is more popular than the other, as there is no common element between them.
Windows users will know AutoIt, Mac users will know Applescript.