Many companies also use his images in their advertisements

(Grammar Questions I Couldn't Answer)

Actually this is a question I did answer in the end.  Although I had to look it up.  I'm posting it here in case it's of interest to anyone else.  Or in case anyone else can give me some more insight.

In class the other day we were looking at the transcript from doing the lesson 7A X-Ray Photographer p.82-83 from Life Pre-Intermediate Textbook.  The following sentence appeared:

"You can see his photos in galleries all over the world and many companies also use his images in their advertisements."

A student raised her hand.  "You told us before that we only use 'many' in negative sentences and questions," she said.  "So why is it in an affirmative sentence here?"

Indeed, I had taught the class this before.  But I had been prompted by the textbook, and my first instinct was to say, "Oh, that's just a rule in the textbook.  In real life, people use 'many' in affirmative sentences all the time."
But instead of telling her this, I told her I would look it up.
So I consulted Practical English Usage by Michael Swan, which stated:

In an informal style, we use many and much mostly in questions and negative clauses.  In most affirmative clauses they are unusual. ...  In a formal style, much and many are more common in affirmative clauses.  Much has been written about unemployment. In the opinion of many economists...(Swan p.332)

I came back and told the student that because the listening transcript was in the style of a report, it was more formal.  And that is why "many" was used in the affirmative sentence.
But let me throw it out to the Internet for comment.  How does that sound to everyone else?