It makes sense to update your site more often, users know to come back for fresh content, and Google likes to crawl sites that update their sites often. Fresh content is also usually more timely and relevant – so makes sense for Google to crawl it.
Interesting piece on statisticians in the Times:
For example, Ms. Grimes worked on an algorithm to fine-tune Google’s crawler software, which roams the Web to constantly update its search index. The model increased the chances that the crawler would scan frequently updated Web pages and make fewer trips to more static ones.