While validationisn't a complete testament to codequality, it does help to make sure thatyour code follows recommendedstandards and canshowyouerrorsin your markup, CSS, and JavaScript.
Now that HTML (and Javascript and CSS) has finally evolved to the point where some basic rich media tasks can be accomplished (e.g. image slide shows), by all means.
While there are many advantages to being built around HTML, JavaScript, and CSS, those tools don't excite game developers who need direct access to advanced graphics hardware to render animations smoothly.