The cloture rules have changed many times over the years. A quick summary can be found on the US Senate webpage. However, Originally the filibuster was not unique to the Senate, House members could also filibuster, and there was no means of voting to end debate. Obviously this had to change if the House was to accomplish anything as it grew. One could well argue that it is time for the rules in the Senate to change again if it is to get anything done.

[1]: http://www.senate.gov/artandhistory/history/common/briefing/...