For ISBNs from the big 5, the number really does indicate the publisher. I think the 5th digit (second after 978) can indicate at least some of the big publishers. Smaller ranges are available for purchase from the brokers. In Canada, the national library will even issue you one for free, if you self-publish.

The ISBN always indicates the country it's from, the United States getting the biggest block, other European nations and Japan getting their own, with Africa, the Middle East, and so forth all getting a block in common.