Really? Is there any evidence of this? Most attempts I've seen at the paperless office have been failures.
Also, even in the attempts I have seen, nobody is writing reports in HTML + CSS. Everything is in Word/ppt/Excel, usually on SharePoint.
What I meant for the html + css is that anchoring your documents to the a4 sheet, while people are consuming more and more content on screens of various sizes and less on paper is somewhat strange. Also google docs are html + css and a lot of javascript :)
Office has great advantage and is not going anywhere soon. But while in 1999 it was impossible to not have office, now depending on your company and employees can go from mildly inconvenient to annoying.
5 years from now - will you worry that some content looks great on paper, or that it looks great on the person's tablet or google glass. If your answer is the second - word is in for a rough ride.
Theres also not much of an incentive to change. Using open source software won't save that much money, and would require training almost every employee. If open source office software is ever going to break its way into big enterprise, its going to have to get widely used by consumers first.