I see know reason why they would be discounted. There are many reasons sites could have the same backlinks. Take ODP listings for example. Or an area that has a couple of solid industry-specific directories. You would expect to see direct competitors listed on the same page.
There was a recent article in SearchEngineLand [searchengineland.com] that discusses ideas I raised in February 2009, a discussion of Link Cliques [webmasterworld.com]. The idea behind Link Cliques is developing a strategy to compete against established sites that are rock solid in the top five or top three, sites with hundreds of thousands of backlinks, even in the millions of backlinks. The method for doing that involves developing your own set of unique and relevant backlinks that point to your own authority to go head to head against established sites.
The idea underlying link cliques is that poaching the competition creates a backlink profile for your site that is derivative of established sites, creating a situation of diminishing returns because you cannot exactly duplicate the competitions backlinks and jump ahead with a partial set of duplicate links. The answer that link cliques suggests is to develop a set of backlinks that are entirely relevant but completely different than the established websites. If you study the top five you will see that many times the backlinks of even the established sites come from unique directions that are exclusive of other sites ranking in the top five or even the top five.
I agree with the previous posts in this discussion that links poached from competitors are not discounted. There is value in doing this and it may get you up to the fifth position if your anchors and landing pages are superior to the competition.
Imo, cherry picking quality backlinks of related sites that are not direct competitors has some value.