Don't be concerned too much on the number of pages that G and Y are indexing. Rather, concern yourself with validating the links they're indexing. I manage a bunch of Wordpress sites and have changed the structure of content here and there. Not paying attention to those changes could lead to diminished traffic due to indexed pages generating 404s. There are probably a lot of SEO tools that can do this but here's a method you can do, on the cheap. If you're using Wordpress, export the links that Yahoo siteexplorer indexed from your site to notepad. Download and install the Redirection plugin from Urban Giraffe (look up Redirection in wordpress.org plugins directory). Use the Yahoo index export and add those redirects into the plugin. This tool is a must have and can save your site from 404 hell!