Ebook formats each have their own limitations. With PDF, you are limited to viewing on large computer screens. And if you are printing from PDF, you might be constrained by the amount of information you can include in extra pages within budget. With EPUB ebooks, the size of graphics and tabular data you could include are limited by the size of e-reader devices.
What if you have large appendices, complex tables, detailed graphics or even want to include multimedia? A website is the most appropriate format for all that "supplementary material". Large file sizes, lots of data—you don't have as many limitations on the web.
With cop-e-boox, you can produce web pages as another ebook product. You can produce a set of pages that you can further design for corporate branding—and you can include "value-added" products to your document (such as links to supporting documents or media).