[nonabelion]

Wikipedia is correct. Radicals do carry a lot of semantic meanings. I think the most apparent examples are the names for chemical elements. For example, the radical 气 means gas. Hellium in Chinese is 氦，hydrogen is 氢. So look at the character you immediately know the natural state of the element. Moreover, even if you don't know a character, if you see it has the radical, you can guess what that is related.