Hi Jubilado,
I think, conditions of the Keris from Madura usually more rough and heavy than the Javanese keris. The iron fibrous more clear and some iron came with many spot. Many keris from Pesisir (coastal) area usually more rough than the other. The pamor pattern of Maduranese keris more bright and coarse. The culture of Maduranese often showing their luxuries or profusion. Same as with the keris which came from there. Strong and the pamor more bright and fully on the blade. Also many pamor demostrated the high skill of the smith.
Trully, many keris with vertical technique of the pamor work came from madura.
The Javanese keris more slightly built. The iron more smooth and the iron fibrous more soft. Especially the keris from old era like Majapahit and Sedayu (about 13-15th century) and the keris from Mataram Sultan Agung period (about 17th century).
But, any keris from Madura which nearly same with Javanese Keris. Usually the keris like this came from Kraton (palace area). See the pictures #5 & 6. This is the Maduranese keris which has the characteristics as Javanese keris. But, we still can distinguishing it by the kind of pamor pattern. The pamor called Dadung Muntir and just Maduranese smith who often created the pamor like this in good conditions.
I think more detail if you see the pictures, because very difficult to me to explain it without example

Also you can see more pictures at my website (
http://keris.fotopic.net). I hope useful.
Detail :
#1-2 = Keris from Madura Cakraningrat on Mataram Era (estimated made about 18th century). The pamor more smooth but the Pasikutan (characteristics) still shown the Maduranese keris.
#3-4 = Keris from Pamekasan Madura. The kingdom which vassal state of Sumenep kingdom (estimated made about 17th century).
#5-6 = Keris from Sumenep Madura which has character as Javanese keris. but the pamor shown as the Maduranese keris.
#7-8 = Javanese Keris from Majapahit Era (estimated about 15th century). The iron is very smoot. Demostrated the very high skill on ironworking.
#9-10 = Javanese keris from Mataram period (estimated made about 18th century). Demostrated the difficult pamorwork and good forging.