They ask that you leave in the notice. You can find it in the footer.php file (wp-content/plugins/wptouch/themes/default/footer.php)
“If you modify it for yourself, please keep the link credit *visible* in the footer (and keep the WordPress credit, too!) that’s all we ask folks.”
The plugin represents 1,000’s of hours of work on our side, and it is indeed all we ask. If you want to remove it from the footer, we can only assume it’s because you don’t want visitors to know that’s it’s someone else’s work. That’s not cool.
I love WPtouch as much as the next guy, but placing a “Powered By” link on the page w/o the user’s permission is against the rules:
4. The plugin must not embed external links on the public site (like a “powered by” link) without explicitly asking the user’s permission.
http://wordpress.org/extend/plugins/about/
