no conjunction for semicolon

Hi,

A grammar book I was looking at told me (literally) that when using a semicolon, no conjunction, like and, but, and so, is allowed. Now taking that as the rule, I saw many cases where a conjunction like "and" is used with a semicolon.

Ex.

He was kind to people; and for that reason the poor people  looked up to him.

Am I encountering a rare but possible case of the mutating-but-now-being-accepted grammatical rule?  

Semicolon (

Punctuation sometimes regarded as a weak period or strong comma and used in ways similar to periods and commas. A semicolon can mark the end of a clause and indicate that a clause following is closely related to the previous clause. A semicolon can also divide a sentence to make meaning clearer. A semicolon is placed outside quotation marks and parentheses. Uses are:

• Separates (but also links) independent clauses in place of a coordinating conjunction or ellipsis, e.g. The package was due last week; it arrived today.
• Separates (and links) independent clauses when the second clause begins with a conjunctive adverb such as: accordingly, all the same, also, as a result, besides, by the same token, consequently, furthermore, hence, however, indeed, in that case, likewise, moreover, nevertheless, on the other hand, otherwise, still, then, therefore, and thus. These usually explain or summarize preceding matter or show some kind of transition, e.g. We organized enough work for the rest of the summer; therefore, I can plod ahead.
• Clarifies meaning in long sentences and in those with several commas. The indication of a strong pause by the semicolon helps the reader understand the meaning.
• May be used before explanation phrases and clauses as: e.g., for example, for instance, i.e., namely, that is - e.g. She is highly qualified for the job; for example, she has worked for more than twenty years as a writer and editor.
• Separates lists or phrases in a series when the phrases themselves have commas, e.g. We visited Springfield, Massachusetts; Keene, New Hampshire; and Durham, New Hampshire.

http://dictionary.reference.com/writing/styleguide/punctuation.html