Actually, since the time of this post, I discovered that technorati’s FAQ covers this issue: they only consider links “created” in the last 180 days. Depending on your blogging system, however, links such as those in blogrolls might get “created” each time you post. Or might not. But in any case, I apparently had 15 blogs that (1) had not been updated or (2) had not linked to me in 180 days. (Or, as Jeremy notes, some could have been splogs. But I thought 15 seemed high for it just to have been that.)