Website Macro-Recorder Prevention? [Example: Facebook]

First question on SO so i'll try to keep it interesting!

Question: I was interested in the technical ability (or non-ability) of a website to prevent macro-recorders from automating tasks on their websites. Is this possible? If so, to what extent? And if so, what kind of algorithms can differentiate a "natural" keypress from one that is sent via a desktop application?

Background: Recently, one of my friends was testing the capabilities of using a macro-recorder to automate the task of sending a personal message to all of his facebook friends. He's a music artist with a lot of facebook friends - not a bot. Nonetheless, obviously facebook does not want this kind of behavior, and to my surprise, my friend reported that he was unable to use a macro-recorder to accomplish this! I myself tried "jitbit macro recorder" which seemed to record the macro properly, but when executed was unable to interact (mouse clicks and keystrokes) with the facebook browser window! Can websites prevent this? Or is there simply a better recorder out there?

Thanks!