I'd never heard or noticed that. Which might those be?
Landmark Legal does a lot of stuff concerning public school education and vouchers. Furthermore, they concentrate on thwarting big-government agendas, whereas Judicial Watch mainly concentrates on fighting government corruption and fraud.
I have never seen Landmark Legal concentrate on the types of cases that Judicial Watch takes on, such as the Loral Shareholder's suit and JW's work with the Discovery process.