the thing is adsense can be better than parking..but it's like going from slavery to indenture servitude...
parking is really dumb for a lot of reasons, but the worst is that you don't get domain age since that is calculated from when the search engines first index the domain's content (and domain age is a big deal in at least google's ranking algo). just throwing up a paragraph of content and a wordpress blog is 1000x better than parking a domain, and takes all of 5 minutes.
i'm guilty of it myself, i have probably 50 domains parked right now that shouldnt be, and that earns me like $5 every six months, but really its not smart.