It's up to the developer to update...

Cnet does not actively monitor for, or acquire, program updates. Rather, it is up to the individual developers to upload their latest versions to Cnet Downloads if they want them to be available through that channel. Unfortunately, the developers of AdBlockPlus have chosen not to submit the latest updates for inclusion on download.com, though you are free to encourage the developer to keep the listing updated.

Regards,
John