I'm not surprised, given how "optimistic" (to put it as politely as possible) the Southwest flight status info is...

As for overruns being more common on Southwest than other airlines: numerically speaking, I doubt it's true. However, because they fly to a lot of second-tier airports (MDW instead of ORD, PVD instead of BOS, BUR in addition to LAX, etc.), they are going to be using shorter runways, on average, than other major airlines. For example MDW is 6500', BUR is 6900', and PVD is 7000', while ORD, PVD, and LAX are all greater than 10,000'. And they're doing this with 737's, not RJs.

Of course, runway overruns are extremely rare because there is a large safety margin used when computing minimum required runway length. So there isn't enough data to say anything statistically meaningful anyway.