If you would closely study the Annexation votes, polling places were established in the population centers / county seats and it was easy for those residents to vote. In the rural areas, polling places were established only in the county seats. Granted, by Texas Law, county seats had to be no more than "one day's ride by horseback" from the furthest point in the county -- but a day's ride out and a day's ride back was a long way for a poor man to travel.
It was easy for the politicos in the county seats to vote -- but practically impossible for the farmers and small ranchers. The figures noted regarding the Annexation in Harrisburg / Houston deal with votes counted -- not votes cast compared to population density. Today, a trip from Spring to downtown Houston and back takes a few aggravating hours -- not two days.
How many folks today would drive from Spring to Houston to cast a vote?