Why would it be more difficult to escape your caste in rural India today?
I believe the phrase "escape your caste" in the question is used to refer to not being subjected to, or influenced by the cultures and customs specifically associated with the caste of a person. Meant this way, the statement about nature of cast system in rural India (as compared to urban India) is definitely true.
We can examine this question more meaningfully by first understanding a few things about the caste system itself. The caste system in India is not about just dividing people in small groups. As a matter of fact it was more about uniting people, and promoting individual behavior that promotes common good of all. Centuries back, when the concepts of democracy and individual freedom was unknown, it provided means to small groups of people to govern themselves democratically, for promoting common good of the people. This also included protecting the group from outside negative influences.
These cast-based self-governing, democratic systems had to be small in those days of limited communication and transportation facilities. Thus each self-governing group consisted of people with similar profession and culture, residing in a small geographical area. The value of such system was recognized by the great social reformer and champion of equality, Mahatma Gandhi. It is important to note that Mahatma Gandhi, who made great contributions to highlight the evils of caste system in India and to rid the Indian society from those evil, also worked to promote the panchayat system which is the old Indian system of democratic self-government in villages.
Unfortunately, in spite of the original values and good intentions of the caste system as explained above, this system also created rigidity of behavior within the castes, and divisions between different casts. This might have been desirable to some extent in the past, but in modern democratic system, and the technological and economic need for integration of people it is no longer so. People in India have been slowly recognizing the negative impact of caste system in current situation because of actions of reformers like Mahatma Gandhi, and also because of the difficulties and limitations faced by individuals in practical life.
In response, the rigidity of the cast system is breaking down with a pace that is proportional to the problems of the caste system faced by people. These problems are faced more in urban areas where people find it more convenient and beneficial to base their association with other people on grounds other than caste. Thus people give much more weightage to factors like education, profession, financial status, political affiliations, business associations, and common interests (say like music). This kind of need for change is felt less in rural areas than in bigger cities, with greater degree of industrialization, commercialization, education, and presence of people of many different caste within a place or institution. This is responsible for the difference in the influence of caste system in rural and urban areas.