Blogger Help : What is the difference between archive pages and the archive index?:
The Archive Index page is no longer necessary as you can easily include your list of archives on the main page of your blog. For this reason, we do not plan to continue supporting this feature in the future. Currently, it is only enabled for blogs which had an Archive Index template as of May 9, 2004.
OK, so your average blog lasts about three months before the writer gives up. But for some of us, we have rather a large archive. My archive page currently has 44 month-based archives. Sure, I want to put 44 links on the main page - that's going to look just fucking great!
Sure it's not necessary to have a separate archive page, but it's sure as hell better than spamming the crap out of your own index.