[TECK]

The way Google works is like this:
First it will send in mission only one crawler, to see if something is new to the site. If the spy detects new stuff, it will report to home base how many links are new. According to this, dependable on each time stamp, the home base will send around 2-4AM it's soldiers (crawlxxx.googlebot.com) in mission to grab the new information from your site.

That's why is so important to have a plain simple link to the archive file on your site. Google say is not necessary and that they will do it for you anyway... but I don't believe it.
Since I placed my archive.php file, I see many more crawlers onto my site then ever, every day. If you have only one folder, they will not come every day to visit your site.
What i did me is this: I submitted to Google the archive.php link. In 2 days my site was hammered hundreds of times by the crawlers.

BTW, this tip (plain link) came from Chen.