For example If you have the following:
Campaign 1 - green widgets
adgroup a - cheap green widgets
adgroup b - compare green widgets
Campaign 2 - blue widgets
adgroup a - cheap green widgets
adgroup b - compare green widgets
Campaign 3 - Red widgets
adgroup a - cheap green widgets
adgroup b - compare green widgets
You'd get a better result if green widgets went to a page designed for green widgets rather than all the different widgets going to one page. Not only is it better for the customer but with the right focus on content per widget you'll increase your chances of getting a bettter conversion rate & in theory a better quality score. This system works perfect in my opinion.
Cheers
You shouldn't be buying AdWords campaigns and THEN creating the pages. Do the pages first, building content based what the site neeeds to become a useful and coherent space. Then, take the individual pages and build keyword groups that would lead prospective clients to that specific content. You're paying for the traffic. Its more important that it converts in to some goal than that it hits the right keywords.
Later on down the line, you can always branch off a few content pages to show relevance for a particular keyword set you're after.