I've never noticed parts crossed out in spam emails (although I hardly ever get them nowadays).
Perhaps your email provider has some sort of filtering system that, wisely, tries to prevent you clicking on 'Unsubscribe' in a spam email. (It's one thing that you should never do. Spammers often simply guess at email addresses, so they've no idea which ones they send out will actually reach people. Clicking on 'Unsubscribe' effectively says "Hey, well done! You've found a real person. Now please send me lots and lots more spam")