Nobel was of the opinion that the peace prize should go to a person who "shall have done the most or the best work for fraternity between nations, for the abolition or reduction of standing armies and for the holding and promotion of peace congresses". With all respect for dissidents, Liu's place is not in this category.
There is no reason aside of the political implications why a dissident won this award. This is just like last year when Obana was awarded the prize. The Norwegian Nobel Committee is composed of five members appointed by the Norwegian Parliament, this says much. Five politically elected people decided to honor an individual from another country that is acting against his country. Liu did not work for "fraternity between nations", not for "abolition or reduction of standing armies" and not for "the holding and promotion of peace congresses". He fights for human rights, but this "fighting for human rights" is something like "fighting against climate change" or "against terror", all of these are arbitrary.
There is a reason why Nobel gave that definition, not because he was stupid, but because he knew exactly who should be given the awards. If this would have been an award for "human rights fighters" then, yes, Liu Xiaobo is on the list, along with other thousands of free thinkers from the planet.