Simsi - 11:36 pm on Jan 4, 2013 (gmt 0)
This dependency thing relates to more than just Google traffic. A lot of businesses depend far more on a third party service than they probably even realise. Whether it be a trading platform like Ebay or Amazon or ad revenue via Adsense... even access to the web via your ISP. If any of those stopped providing you with their service right now, a lot of online businesses would struggle, many might not even recover.
One issue is that, because making money online has pretty low barriers to entry, it can mask the need for applying traditional business principles: building relationships and spreading risk being the two that immediately spring to mind. Making money does not equal running a business.