The most basic response you'll get to this question is that tables are meant for tabular data while table-less styling using xHTML/CSS is used for layout.

When coding table-less, it's not just about using CSS and avoiding the <table> tags... It's about making the site Search Engine Optimized (SEO), making the code semantic (for screen readers), and increasing page loading speeds while minimizing the amount of markup used in the code.

All of this can be argued one way or another, but in general; that's your normal response to such a question.

And yes, many people have created a site "completely table-less"; it's not hard.