When we think of races that have been included in Player's Handbook or Campaign Setting versus the Monstrous Races we often make a distinction in how those races act and live. The Player Races are more civilized and the Monstrous Races savage. The printed material often backs this up to a certain degree, and may even change their stories a bit when it becomes time for a Monstrous Race to become a full Player Race. Jared von Hindman comments on this with the Minotaur in a recent article for Wizards' website.
Our own prejudice against monsters often takes this on even further though. In 3.X, where I started DMing, one of my biggest grievances was with the low Intelligence score on the Minotaur. I didn't like the idea that all Minotaurs were savage brutes. Even if a minotaur wasn't nice, it should at least be cunning. This understanding has been allot more popular as well, with the popularity of World of Warcraft.
Other races have received similar, or reverse, treatment with setting. Orcs, one of the most loved Monstrous races, is also the one most relegated automatically to savage, but not so with Eberron Setting. The halflings who are so often associated with the peaceful hobbits of Tolkien, are brutal, and dangerous in Dark Sun.
So how do we define a Monstrous Race? It becomes especially difficult with a point of light campaign. No more do goodly races from large kingdoms of peace and light, welcoming in outsiders and defying evil. The norm now is to distrust outsiders. Adventurers approaching a small town they have never been to before are likely not to be let in without some intimidation or bribe, never mind being welcomed. They may even be attacked on sight.
Is this so different to a pack of gnolls ambushing travelers who had wandered into their territory?
If its not your level of aggression towards outsiders is it simply the fact that you live in a city that makes you civilized? I find it hard to label all nomadic or tribal people savage. I use catfolk (in 4e use shifter stats) as a tribal people that most people would find quite civilized.
4th edition has made a big step towards keeping more and more races unaligned. Every race, like every human, can run the gambit. I favor this lingering gray, though certainly plenty of people oppose it. They would very much prefer it to be the good guys vs the bad guys and leave it at that. That can certainly be entertaining. We all like to be heroes at times. I like to make my heroes work a bit.
Just some thoughts for now. If you liked this article check out the one I linked to above and Chris Simms' writing on the nature of canon.