Includes, CSS and XSLT are great technologies and I often use them in conjunction with SiteMesh.
However, as mean of separating content from layout they all have some distinct issues that SiteMesh overcomes.
Include technology requires the content to be aware and directly tied to the presentation. Furthermore, it often results in a fragmented presentation.
Cascading Style Sheets promised to remove presentation from content. For the most part is does a great job. However,