MVC (or OO) is not a guarantee against bad code, but it does provide some necessary structure, especially for large, extensible projects. Other patterns can also be utilized, but some kind of pattern needs to be implemented. Wordpress had no logical pattern to it's implementation.
Also, MVC wouldn't make sense for the Linux kernel, but it would make a lot of sense for a major CMS.
Also, MVC wouldn't make sense for the Linux kernel, but it would make a lot of sense for a major CMS.