I like yahoo too. Although it hasn't changed much over time, yet I find its services satisfying. As far as popularity is concerned, I believe yahoo is still ahead of Google.
I like Google's start page. its simple yet powerful. While, Yahoo has a load of content on the index page and its not that of useful for me or everybody. Well Yahoo should change their portal page , but in a complete diffrent way , not as like Google.
google focus on search. but yahoo focus on search and content provider. If yahoo switch to google, it lose many ad income. that is bad news for yahoo itself.
It is important for search engine to be simple and yet powerful but it has no big purpose to look as Google. It is bigger concern why Yahoo crawls less urls than Google. Yahoo results are loading much more data becouse of special effects and javascripts so browsing Yahoo results every day will have result that you will load much traffic on your connection, not so good for people who have limited connection traffic or slow connection. Another important thing is why Yahoo requires yahoo account for every little thing that you want to use on Yahoo service.
If simplicity works for Google, and the portal look works for Yahoo! then why should one change to look like the other?
I agree, they don't need to change their look. Google is nice for their simplicity. Yahoo is nice because of it amount of information shared and the design. I don't think that they will change it.