Based on the Giants runs scored vs. runs allowed, the Giants expected wins at this point is 46.9. Their actual wins are 46. So they have not been "lucky" in terms of wins and losses. Their 303 runs allowed is the best in baseball. The pitching has been awesome. The offense has been middle of the pack, but hey that is not as bad as many (including me) expected. So the Giants are for real because they have the best pitching in baseball. Will this continue to be true in the second half of the season?
It is not a slam dunk. Lincecum is even more dominating this year than he was last year when he won the Cy Young. Some people worry that he is pitching too many innings given his age, but I won't jump on that bandwagon. He is one of the Giants' two All-Stars. The other is Matt Cain. Now I love Matt Cain. He is from Dothan, Alabama. That is just two hours north of my hometown in Florida, and is where my brother lives. However, Cain has been a little lucky this year. On balls put in play, Cain's batting average against is a little. Plus he's been lucky with stranding base runners. If this luck does not continue, then you can expect his hits allowed and runs allowed to both jump up a bit. Cain's a flyball pitcher too, so a jump in home runs allowed is always possible. Randy Johnson has been ok, but more importantly healthy. He just suffered his first injury of the season, which does not look like it will be too bad. However, it's hard to expect him to stay healthy the rest of the season. Barry Zito has been better than last year (which is not saying much) but could actually do even better in the second half. The fifth spot in the rotation has been in flux, so things could really only get better for that spot.
Enough about the Giants... As for the rest of the NL. My favorite team, the Atlanta Braves, are mediocre and there's no reason to expect a lot different from them. The Phillies are better than their record, while the Marlins are a lot worse than their record. The Cardinals are also not quite as good as their record, but the rest of the NL Central is very mediocre. The Rockies have been a huge surprise, and they look a legitimate contender for the wildcard spot. They should be the strongest challenger to the Giants, and of course the two teams will get plenty of chances to play each other as they are both in the NL West.
As for the AL, arguably the four best teams are all in the AL East. The Yankees have a nice lead in the wildcard over Tampa Bay. Still, Tampa Bay has proven that last year was not a fluke. The Yankees are definitely getting a nice ROI on all the money they spent on pitching. They are only a game back of Boston. Both teams look to improve in the second half. The Yankees will get three months of Alex Rodriguez, and the Red Sox's David Ortiz seems to have finally regained his form. The AL Central is a mess, with three pretty good teams within 2 games of each other. It's easy to count out Minnesota, but statistically they have been the best of the three teams. Finally, the AL West is a two horse race, and the two teams, LA and Texas, are statistically very even.