The beauty of it is they can accomplish essentially the same task without having to do that - by identifying common alpha-numeric data in the page and using it to create their own links in your page.
Some of the possibilities include highlighting and linking UPC codes, manufacturers' part or model numbers, Swan catalog numbers, commonly identifiable alpha-numeric data found in technical specifications - such as parameters for RAM modules (512MB SODIMM) or other PC specs.
Every time I ask myself the question - "Would Google really do that?" Afterall, the function is currently limited to mapping and ISBN's. While I can't answer in the affirmative, I can't say no either; because if Google's intentions with linking book data were truly altruistic and if they truly wanted to help the user, they'd be linking ISBN's to Library of Congress or libraries with volumes to read online, not a commercial entity.