If you watch enough of these Live Lines you will see (especially in the NFL) they tend to go very heavy with one side (the side that looks good at the current time) especially with Overs and Unders in the NFL and can get some really good lines.
Example again last night a quick 14 points were scored by atlanta and the Over under went to something like 48.5 + 175 for the under. Also Jets were +20 at one point as well.
Tonight too +1800 for the White Sox. I know 4-0 is steep especially with Oswalt but he hasn't looked as good as previous outings. Part of that may be they are squeezing him a little and part may be he just is not as sharp. Also could have gotten CWS +4 runs -127