According to a posting on google’s blog, they have altered the size of the search buttons and entry field as it ‘it symbolizes our focus on search and because it makes our clean, minimalist homepage even easier and more fun to use’.

It’s the latest in a long cycle of Google home page changes, that can be seen here on their time line.

Full posting on the Google Blog.

Now -S-U-P-E-R- Sized.

For us, search has always been our focus. And, starting today, you’ll notice on our homepage and on our search results pages, our search box is growing in size. Although this is a very simple idea and an even simpler change, we’re excited about it – because it symbolizes our focus on search and because it makes our clean, minimalist homepage even easier and more fun to use. The new, larger Google search box features larger text when you type so you can see your query more clearly. It also uses a larger text size for the suggestions below the search box, making it easier to select one of the possible refinements. Over the past 11 years, we’ve made a number of changes to our homepage. Some are small and some are large. In this case, it’s a small change that makes search more prominent.

Google has always been first and foremost about search, and we’re committed to building and powering the best search on the web – now available through a supersized search box.