I hesitate to cast doubt on Business Insider, but the article you quoted offers nothing reliable.
It quoted a small business owner as saying: " ... generally 50 to 70 percent fail within the first 18 months". But it gives absolutely no indication of where that figure comes from or how reliable it is. It sounds like too vague a statement to be trustworthy.
It also says, " More than 200,000 small businesses closed between 2008 and 2010 ..... according to U.S. Census figures." But that's no indication of how many businesses failed. It only says how many closed (which might be because the owner retired, or the company was taken over by a larger firm, or a dozen other reasons). And in any case, it can only apply to businesses in the US, which might not be typical of the sector as a whole. Also, the original question was about the number of businesses that fail in internet marketing, which again might not be representative of the entire small business sector.
In summary, don't put any reliance on vague statements published in articles without any corroboration, details or sources.