Overall, semantic does convert text to semantic markup, however, you need to code it yourself, mostly (using subheadings and lists).

Also, plenty of stuff depends on the theme you have chosen. As you can see, the theme I use is partly built on tables, which isn't that bad, since it uses CSS anyway. Largely, it uses semantic markup (subheadings).

To make Drupal more SEO friendly, you can:

• select a theme with semantic markup (HTML/CSS, subheadings, lists) and make even an accessible one (search for 'accessible drupal theme'
• use subheadings in posts on your own, as well as write your titles using the words, related to your post
• use clean URLs, select categories/topics carefully (maybe even create a custom taxonomy name, such as "Topics" here)
• add URLs that show duplicate content (such as comments, feeds) to robots.txt that comes with Drupal - you can check my robots.txt, for an example

Overall, it means knowing your audience, words your audience uses and use them throughout your website.