In museums, research facilities and universities throughout the world, there are tens, if not hundreds, of thousands of human remains held in collection. The Smithsonian Museum of Natural History alone has more than 18,500 human remains in its collection. Most of these tend to be the remains of indigenous peoples (read: non-European) whose remains were often come by through illegal digs (read: grave robbing).
The concept of burial or entombment or some such means of placing the body of the dead away from the living with the idea of allowing them to rest peacefully is an ancient one. Evidence of storing the bones of the dead first pops up 300,000 years ago, and it looks like around 90,000 years ago the concept of intentionally burying the dead was first adopted by the Neanderthals. So we've got between 90 and 300 millenia of cultural tradition that when a person dies you sequester their dead body and leave them there.
Indeed, the concept of the potter's field shows how strong a responsibility society feels toward the dead. The City of New York maintains six potter's fields -- cemeteries for the indigent and unclaimed -- and has since the early 19th century. In 1941, the city made it official, creating a mandate that it must carry out the burials of its unclaimed residents, has it had been for more than 100 years. One of the fields, Hart's Island, is the largest cemetery in the U.S., holding the bodies of more than 800,000 people. (Here's a really awesome photo spread of the abandoned areas of the island.)
The idea of digging a person up in the name of science is far less established temporally. In fact, the field of archaeology is relatively young; Heinrich Schliemann is credited as the father of modern archaeology for his excavation of the lost city of Troy in the 1860s.
The gathering movement toward repatriation of old remains is based on the idea that the dead have a moral status like they had when they were living. This leads to a massive implied indictment of the scientific fields of archaeology and anthropology. On the one hand, they need to be able to study graves to learn about the culture to which the deceased belonged. On the other, one can reasonably accuse both fields of being technologically lazy, using techniques that Schliemann established two centuries ago to effectively remove an entire site either bit by bit or wholesale for study later at a facility rather than pushing their fields to create less disruptive techniques and technology that allows for in situ (and more respectful) study of the remains and accompanying grave artifacts.
In addition to the pressures put on the dead to get up and make some money for the living exerted by anthropology and archaeology, there is also a lot of pressure to not stand in the way of progress. Humans today are quite fond of building roads and the like and this requires digging. Sometimes road crews happen upon undiscovered archaeological sites, and perhaps a 1976 incident in Iowa sums up the mentality regarding remains we have in the U.S. The road workers found 26 Caucausian skeletons and one Indian woman's. The Caucasian skeletons were reburied elsewhere; the Indian's remains went to the University of Iowa for study.