The style builder is built in a way that it does not require .NET knowledge - primarily for designers and front-end developers - and is an online tool
, so it doesn't require Visual Studio. (the requirements are only Firefox 3.5 or Internet Explorer 7/8 and Silverlight 2). Therefore, they can safely change the styling of the controls (without learning all control-specific styles) and fine-tune what they want in the exported CSS files (the style builder exports plain CSS + images, after all).
the Telerik team