I was thinking something is missing from this article, and whats missing is the reasoning why joins are generally better than sub queries. The reasoning give you more knowledge of why and when you should use joins as opposed sub queries. It would be erroneous otherwise.

Having an Oracle background the answer comes to me quite fast. They are better because they can be used by the optimizing compiler to reduce the amount of data that the database has to go though to get the answer.

Thus if the solution requires that the database go though all of the data then a sub-query might be better because a join may force the use of an index, and in that case you are traversing the index and all of the data, such as joining a large and small data set in addition to requiring all of the data from the larger data set.