martinibuster - 4:28 am on Nov 6, 2010 (gmt 0)
Could it be that it is your particular industry...
I can only speak from my experience, but I find that niche can have an effect on the success rate. An informational site that is useful may have a higher success rate than a shopping site that is useless except for buying things.
Another factor that can limit a link begging campaign is the choice of sites to approach.