Run Spreads... What do they mean?

I was checking out the standings today, and I noticed that the Royals have scored only 5 more runs than they've allowed (49 to 44).

Contrast that to the first place Chicago White Sox who have scored a whopping 75 runs and have give up 52. That's a nice 23 run difference.

Here's a surprise: The Boston Red Sox have scored 66 runs, but they've also allowed 66 runs. Yet, they are 9-6 and are in first place.

Talk about an ugly start. The Tigers have scored 50 runs, but have given up (get this) 92 runs. That is by far the most allow so far this year (The Pirates are next at 80 runs allowed).

The Diamondbacks lead all of baseball in runs scored with 89.

I'm not sure what all this means this early in the season, but it is kinda interesting to look at.