Since some versions the folks at wordpress.org have created an automatic update check inside their software. This is not only liked, it does create more load and slows down your blog. but rescue is just around the corner, take this update as a booster pill for your blogs speed:
http://downloads.wordpress.org/plugin/disable-wordpress-core-update.zip
It disables the core wordpress update routines, resulting in an overall faster Blogging Experience.
