There is one very good reason: the people you are about to employ in 5 to 10 years are born and raised on web 2.0 stuff. So if your company does not start now with adapting to an enterprise 2.0 style nobody will work at your company in 2015. The battle for talent is getting more intense every day. Not offering the approperiate tools and stuff in the office will destroy your competitive edge on the labor market.
Of course this is just one reason your company should start, there are some others like: knowledge transfer, getting the whole world to work for you practically for free, building your network etc etc.