* It's a good idea to try to quantify the cost of losing an employee. If you at least understand what basic costs you'll incur, such as cost of hiring, training, etc. it'll give you a basis for realizing the importance of minimizing turnover (perhaps you'll even conclude that turnover isn't a big deal in your case). But it's very hard to quantify some of the largest costs such as employee moral. I was once at a company where an entire (small) team slowly left after a single person departed. Perhaps any individual's departure could have been handled without too much of an issue, but the loss of entire team and all the institutional knowledge contained there was quite damaging to the company.
* The article mentions some tips for retaining employees and I think they are spot on. But I don't think it emphasizes the importance of salary enough. A lot of employees jump ship because of the higher salaries they can get when they move around. Meanwhile, the original company they left will likely have to pay market rate to get someone with similar experience (and none of the institutional knowledge), so they would have been much better off if they would have just bumped their employee's pay to market rate in the first place. By the time it gets to a counter-offer stage, it's often too late.
EDIT: The article briefly mentions the importance of paying market rate salary, but I missed this sentence when I read it over the first time. Updating my second bullet accordingly.