Pretty doesn't cut it anymore. Web design used to be about making a page attractive on a desktop monitor. Now users are browsing the web with tablets and smart phones. In addition, search engines and many users, including the disabled, depend on software to interpret site content for them.
The standards for good web design have changed. The biggest difference is the separation of style from content. How does a site look in a text browser with the images turned off? If your navigation menu is made up of images and images are turned off, how will one navigate your site? More and more people are looking for information on different platforms and if your information is not presented well and functionally to everyone, your site is not working for you as it should.
Spaghetti code, nested tables and outdated markup can triple the bandwidth required for even the simplest of websites. This means that users are forced to wait longer for your pages to load - increasing the chance that they'll bailout before they've even seen your logo.
Does your site look different in different browsers? Or do you create a new version of your site every time a new browser or device is released? Designing and building with web standards lowers production and maintenance costs. Make design changes in hours, not weeks.
When designed and built the right way, any document that is published on the web can work across multiple browsers, platforms and devices, even those that are yet to be built or even imagined!
Because standards are inclusive by nature, standards-based design accommodates people who use older browsers and devices.
Comply with accessibility laws and guidelines without sacrificing beauty, performance or sophistication.
The good news is that adhering to standards not only accomodates all browsing devices and makes your site accessible to all, but it is the foundation for good SEO!