Why use tables to structure your layout?

Question

Looking at the source code for Stack Overflow, I noticed they have used tables and inline CSS quite a bit, also something I found odd was use of inline table attribute forma

Answer 1

Tables and layout

SO's layout is not based on tables.

At a quick glance, I'd say SO layout is 80% div-based and 20% table-based. Tables are used in the header and on the "badges" box. Table use is appropriate for badges IMHO (it's a list of items, after all), not so good for the header.
Anywhere else, divs are used.

Inline CSS

Again, many inline definitions are used (probably to quickly mockup site's structure), but SO correctly uses also css (to style the divs and to provide print formatting).