I've experienced this as well. I think its a program thats integrated into your web browser and acts as a "key word" type of application. Meaning that when a specfic word is used it is underlined sometimes and can be used to access topics related to the word. "Jobs" for example.
I don't think this has anything to do with typos or a program which corrects mistakes or underlines them. While I haven't actually clicked on such an underlinded word, I would assume it leads you to a directory based on the word.
Its little more than an application that was installed within the web browser. Therefore you may or may not see these underlined or highlighted words if you are using a browser which doesn't support that application or hack, or you haven't upgraded to the most recent version of that browser.