The American Chemical Society (ACS) has a typesetting standard for publications. This ensures that all the structures are the same size. Having chemical structures that are different sizes in different figures looks absolutely awful and unprofessional. The sizing standard is 75% reduction of the ACS 1996 standard stationary used in CambridgeSoft ChemDraw. MSWord and MSPowerpoint can do this no problem (however MSWord and Powerpoint 2008 have broken the ability to cut and paste back into ChemDraw - this bug is an issue with word and powerpoint, not ChemDraw - Awesome). Pages and Keynote cannot. They insist on handling the graphics by pixel, inch, centimeter, whatever.
EDIT: Scaling the images in ChemDraw before moving them to word or page or keynote, etc, does not work. It's not that simple. The reduction must occur within keynote and pages.