Again it also goes back to the point I made in an earlier post in this thread, and several other posters have touched on. How the hell do you get the away supporters to sit down at all!?? It seems very hypocritical to really get tough on your own fans, and let the away fans stand. I think if the stewards tried to make that happen, there would be a full-blown riot pretty much every game in the away end! Hence, that's why it still happens at pretty much every match in this country.
And there is the problem - the club will target home supporters because they are identifiable and can ban them easily. The most they can really hope to do to an away supporter is kick them out but that often leads to more conflict ( such as Bolton ) so it's often easier just to keep them in the stadium ( where you have some kind of control over them ) and turn a blind eye. I'm not saying it's right but as yet nobody seems to have come up with a better solution.