Like a rock thrown in the water that generates a ripple, the first circle is much clearer, stronger, but as the ripple generates and spreads out, it also diffuses and lessens.  It seems to me that this is the same with Buddhism, because as the teachings move farther away from their original source the potential for those teachings to be altered or misunderstood also grows exponentially. 

         As I understand this process, it seems to work something like this.  The Buddha turns the Dharma wheel and teaches his students.  Many years later those students got together and collectively decided on what the Buddha taught, and recorded those teachings.  Given the different capacities of human beings, these teachings have been modified and changed overtime, sometimes censored and sometimes sanitised to fit in with people's understandings and expectations. 

         This is compounded by the fact that many students have not had their own realisation and so, when they tried to understand the Dharma, they literally reduced that Dharma to the level of understanding that they had. 

         Then outside scholars came along, and in the west for example, linguists of noted ability may attempt to translate into English works from various languages and schools [bearing in mind that each school's texts reflect that school's understanding and particular bias or world view). 

         Now while such linguists may have exceptional language ability, they more often than not lack a true understanding of the Buddhist terminology that is employed, and have not studied Buddhism or undertaken any Buddhist practice, and therefore have no grounding in Buddhist doctrines from which they can base their translations. 

         One example of this is the translation of the Diamond Sutra, where modern translators may rearrange the order that text appears in the sutras to conform to their own understanding or linguistic preference, not realising that the sutra is a Mandala and is necessarily recorded in a certain way, for particular purposes.