Traffic analysis does not require decryption. Someone watching the traffic can still see that you are on Wikipedia, what time you were on the site, how long, and the approximate size of the content you downloaded...or uploaded for that matter.
Say you submitted a post; even encrypted its still possible to see that more bytes were sent than in a normal GET request. Even if your IP is hidden behind your WP login, it is feasibly possible that the timestamp combined with the approximate byte count could be used to identify you. Of course, HTTP keepalives would make this more difficult, but other tricks like checking the referrer header when clicking off to another site could betray you. Even if you are just clicking around, it could be possible to establish a fingerprint of your traffic pattern, using things like byte counts, number of concurrent connections (to identify the number of images on the page perhaps?), etc. that could be used to identify the pages you visited.