ABC has taken a lot of heat from viewers about their scheduling of "Lost," with all the mid-season repeats, weeks off-schedule, and so on. I heard that they had learned their lesson, and that "Lost" would appear more regularly during the next season. The plan was to show several weeks of episodes, then take several weeks off, but they would keep viewers informed about when the new shows would air.
Summer used to be the season of re-runs, when viewers could catch up with missed episodes, but not any more. Networks are more likely to show re-runs during the Thanksgiving and Christmas holidays when viewers are too busy to watch new episodes (that was formerly the reason for summer re-runs as well - people watch TV less during the summer). Now, like you, I'm mystified by the networks' approach to scheduling. It's just nonsensical to move shows or change their times with no notice, and to fail to show re-runs of popular shows.
Contrary to what some people have said here, it's my guess that ABC is trying to build viewership for George Lopez's show in order to boost its ratings during the regular season. The Lopez show was a poor lead-in to a show like "Lost," so I hope ABC re-vamps the whole lineup.