AFAIK, WOFF is the only font format that is specifically designed for web browsers. So I assumed it was the only font format that could be relied upon to work consistently across browsers and platforms, and so designed Construct to focus on WOFF support. (You can still import and use other font formats, but Construct will always prefer WOFF if it's available.) That was little more than an assumption though, I'm not sure if other formats are consistent or widely supported, but I thought choosing WOFF would minimise the risks of compatibility problems.