Hopefully this post doesnt start a Table v Div (Yes Div not Dev 😉) war.
Tables werent made for designing, basically back in the day they were used for tabular data eventually developers abused the use of Tables by thinking that it would be great to use them for Design eventually this became the mainstream use for tables.
The reason for the browser compatibility issues is IE (I think ive started it), IE doesnt support CSS correctly so hacks are required probably why CSS / DIV layouts are still taking there time on the web. Now tables may seem like the easy way to fix this problem. But what happens when you want a 2 Column Layout and you have a 3 Column Layout? Yes thats right you need to re-code all them pages + CSS if there is any, while a correctly implemented DIV / CSS site will only need the CSS fixed, CSS ZenGarden is probably the best example of Div/CSS working correctly content is seperated from design so we can have multiple CSS Themes as they have.
There are a few major sites preparing Yahoo has started but it still has quite a bit to go, AOL is probably the only Major site that I am aware of that is Div/CSS.