From our experience we know that if with in the first 20 days of building the comments the links are not removed truly chances that they get deleted by the admin of the blog or the moderator aren't there.
With this say imagine that we build a blog comment and on day 19 it is removed. We'll we are forced to create a new one (to replace) and guard the link for another 20 days.
So the point here is not to sale things that get deleted in 20 days, but to sale links that we know will stick there for the long run.
Cheers!
