CSS has two levels, CSS1 and CSS2. Level 2 notably includes absolute placement and generated content.
Unfortunately, even CSS1 is not fully implemented by 4 generation browsers.
The half-assed implementation in Netscape 4.7, for example, may lead to perfectly legal CSS producing black text on black background. The user loses.
The only browser that completely implements CSS1 is (and I say this with great bitterness) Internet Explorer 5 for the Macintosh. It even implements some really tasty bits of CSS2 like generated content.
The current situation, with 4 generation browsers still being widely used, forces Web developers to remain in a "core" set of CSS functionality, which certainly sucks.