They play up with the big boys, get to do the same stuff the big guys do, talk about the same stuff the older kids do, and might in the end gain some maturity. Along with that, they get twelve or thirteen new friends. Again as a player agent, the friends thing juts doesn't hold true. Kids have a wonderful ability to keep race, sex, looks, ability, and other trivial factors from getting in the way. Now go look at your average adult cocktail party and see the difference.
Kids have that wonderful ability to adapt and fit in that adults often loose.
Don't worry about the friends thing too much unless your son is really concerned. I seriously doubt he will be too concerned if he also understands that he will get to play real baseball with the big boys. As for Phil's post, I wish there were more kids like that around. However, I never see pick-up games around here and rarely see kids out playing catch. My son would love it if there were kids in the neighborhood to play ball with, but most seem to want to hang out on their Razor Scooters and trade Pokemon cards.