JonBMX3 - 9:43 pm on Oct 4, 2012 (gmt 0)
I agree with martinibuster that there is probably more going on - even just regular link building month over month.
But certain well aged directories still carry value. What I would recommend doing is seeing if a directory page from that domain actually ranks for some of your target keywords. This is especially the case in some B2B silos with limited authority web properties (sans businesses).
And while this isn't the perfect solution, if you can uncover a hub (more than 2 or 3 of your competitors having a link), its probably not a bad idea to have a link there, also.