That is like comparing apples to oranges, or even Mac's to PC. Each one has their own way of doing things, and anyone saying that one is better than the other is simply their opinion, nothing more. It's not about what you don't have, it's about what you do with what you do have.
2 different companies, and while both may offer similar services, both are known for different things.
Both are obviously known for their search engines, but things that are notably different about both are:
Google's company reputation regarding privacy and their search engine technology, not to mention worker innovation and the simplicity of their search engine, and Gmail. They also have slowly but surely expanding over the past few years, and they tend to be seemingly more cautious about what they step foot into, but when they do step into the area, it tends to be in a complete and stable, almost perfect way, not holding back, which makes a lot of other companies nervous I think. They also tend to not deal with outside companies very much.
Yahoo's overall features, such as news, weather, maps, yahoo mail, yahoo messenger, integration with microsoft messenger, and overall what they do as a company, as they are an all around kind of company that tries to branch it self out in as many ways possible, big and small, with plenty of partnerships.
So as you can see, each one is known more for different things, and like I said before, it's like comparing apples and oranges in a way, other than both are .com companies and both originated simply as search engine portals, and both are expanding their horizons as far as what services can offer. I wouldn't exactly say one is any better than the other, as I use each for different things myself.
Example: I prefer Yahoo mail more than gmail, but I prefer using google's search engine over yahoo's.
Hope that helps.