Many people think their commercial compost is great because stuff is doing better with it than their stuff did with cement-like dirt. That compost probably has persistent herbicides in it that is stunting plant growth. But the only way to know for sure is to grow a bunch of plants next to same species/variety plants that are grown in compost that definitely doesn't have it.
http://www.youtube.com/watch?v=GunQ9mB0ywU
Good info!