It is used now because it is a lot more structured. It promotes the proper use of Headings <h1>, <h2> etc... and others. It means that Tags are only used for thier intended purpose.

For example. If you were going to write a letter, you wouldn't use Microsoft Excel, you'd use Word. Same thing applies here. You should only use tables for displaying TABULAR data.

Modern web design dictates that content and style should be kept separate at all times. Anything that pertains to the way a page looks should be in the Style Sheet.