Many marketers are reluctant to “share” their hard gained PageRank with other topic related websites, through outbound links. Excluding competitive reasons, their concerns are summed up in these two:
1. bleeding to much PR that there isn’t sufficient left to fuel their internal linking campaign; for muting the monkeys which preach PageRank bankruptcy by outbound linking, I suggest reading this article on DailyBlogTips.com on how linking out will NOT reduce the Google PageRank of your pages.
2. linking out to related websites will often times determine massive returns of favour from the linked to webmasters, thus clouding your link network with a tone of reciprocal links that, makes Google believe it’s witnessing blackhat SEO in action.