I suggest you read this article, http://www.joelonsoftware.com/articles/LeakyAbstractions.htm...
PS: The article that you suggested is written by a guy that tend to speculate over his point of view without taking in account the reality. In all modern RDBMSes queries having (a=b and a=c and b=c) will be simplified by query planners (Oracle and Postrgre do it) so there will not be any difference in performance.