In one of his blog posts, Barry Schwartz talks about the confirmation by Google, on the same treatment of "/" and "/index.html" in the URLs. The topic has become a hot debate in the Google Webmaster Forum.
Googler, JohnMu, confirms that both "/" and "/index.html" in the home page are typically treated the same by Google. He also said that with or without these server header responses (301s, 404s, etc.) will remain the same.
However, Google will treat these headers differently only if the webpages have different content. The news has really surprised many webmasters who had no clue about them so far.