The reason for preferring XP Pro is account security. It is much easier to lock down all the accounts. For example in XP Home, as far as I know, the admin account is always accesible – just boot in safe mode. From there you can do anything you wish to access any files.
My concern is over securing the netbook so that if it is stolen the thief will find it hard to get at your personal stuff. I know someone somewhere will always get in but Id like to make it harder for the casual thieving git lol!