I don't think anything is wrong with the <strong> tag. It is interesting that it is listed next to the <b>/<bold> tags, as <strong> is often suggested as a semantically correct alternative to those tags to denote the importance of a specific bit of text.

Perhaps the author feels that only <em> should be used to place "emphasis" on the text in question, and that it should also be used instead of <strong> as strong doesn't give as clear an impression of importance as <em>.

I think you are just fine using <strong> in places where it is appropriate.