Its not true that all business mans are showing interest in facebook promotions. I think you also know that social sites are playing huge role in SEO and people are doing all things together because depending on one thing will never help your business. All are focusing on all major things like social sites, using adwords, creating unique content, building quality links through many ways. So promoting on only facebook will never solve your problem.
Social Networking has also become one part of SEO in a way now. But it is not true that companies are investing more in Social Networking and not in SEO. Sites are still getting more traffic from search engines and that is done through content creation, backlinking, etc.
Due to have use of smartphones people use social networking website on the move so Social networking websites can get huge traffic now a days. However SEO is a long term process and can get you traffic for longer time. Both SEO and SMM are liked by business man for promotion.
Peoples search their needs on Google as well as Facebook, Facebook is the greatest way for product promotion and their are a lot of people are traveling, so more business man are showing their interest on Facebook, Facebook Marketing also a part of SEO.