Ghosts Spin Me Right Round, Baby, Right Round, Like A Record...

Last night T and I were watching some Haunted History episodes when it occurred to me that the vast majority of "true" ghost story TV shows, documentaries, and books I consume seem to concern ghosts from the late 1800s.  Why are there not more ghost sightings from other periods in history?  By a simple years-on-this-continent standard there should be far more Native American ghosts than there are rich people from the 1800s.  And yet.  Was there something about the late 1800s that produced more ghosts than other time periods?  Do ghosts wear out after a time, so in the late 1800s there were primarily ghosts from the late 1700s, now we have the late 1800s/early 1900s ghosts, etc?  Does that mean that circa 2085 there will be nothing but ghosts with big bangs drinking New Coke?  Inquiring minds want to know.