Bingo.
And why do it?
As strange as it may seem, there are a lot of people who won't touch a product that they COULD use with little difficulty if it's not for their game system. I'm not one of those on certain types of books like sourcebooks. (Adventures on the other hand... I generally tend to avoid.)
Stamping it 4e could expand the product base. Now, wither it could expand it enough to justify antoher print run of a different product, that's another question that I don't know the answer too.
One unorthodox way of doing this without doing another printing, would be to make a deck of monster cards from the Paizo books like "classical monsters revisited", "dragons revisited", "dungeon denizens revisited", "classic horror revisited", etc ... with the monster statistics in 4E format on the cards.