I’m pretty sure the desktop version of Yahoo! Messenger is exactly the same as the web version. I used the iOS app and it has no interesting features, either. It doesn’t even have video chat, I’m not sure if the older versions of Yahoo Messenger had that either.
The UI reminds me of the new mobile Skype design, as well as other mobile texting apps. Do many people even still use Yahoo! Messenger? I don’t know any people who use it anymore. Even the people I know who still use Yahoo! Mail dropped it years ago.