A wired article on why hardcore gamers love peggle finds a strikingly simple way to categorize gamers as casual or hardcore. It's a short and good read, check it out.
In summary the article proposes, based on Popcap games data and theories, that gamers either put effort into understanding complex casuality or they don't. Hardcore and Casual. Which would explain the difference in appetites as well as time invested and similar data available from this kind of categorization.