This is not the only experiment for Google Suggest: other changes include the direct access to the top result for navigational queries, direct answers and suggestions from your search history.
Since many people replaced the address box from their browsers with Google's search box, it's natural for Google to make the search box more powerful and to provide even faster access to search results. If Google's search box first became ubiquitous through Google Toolbar, then Google Toolbar's search box evolved into Chrome's Omnibox, the added functionality should now be included in Google's homepage.