Famously, Amazon redefined the purchasing experience for books, you can now order almost any book and receive it with in hours or days. They used digital methods to change the industry. 

Watch out! Goes the mantra, or you'll be next.

Even in Professional Services you need to be able to compete by marketing & delivering your services in an easy way for your clients to engage with - and if you don't then the Amazon's of your industry may end up making off with 50% of the global pie leaving everyone else fighting for scraps. It hasn't happened yet but firms like one year-old Atrium in Silicon Valley have raised $65m to do exactly that. Digital offerings do pose a very clear threat. 

But maybe the more important lesson is not books but ebooks. Amazon do not have 50% of the ebook market, they have 83% (of 487m ebooks in the US). Basically the whole lot - the rest being Apple, Google, Barnes & Noble and a couple of others. And within 3 years of launch those ebooks represented 25% of all book sales. 

The traditional firms are barely represented - they could not & cannot compete. That is the really scary idea for professional services; not that others will eat your lunch if you can't compete on-line but that when new business models are developed then those without a strong digital presence will not be involved at all.