Why does Xcode 4.2 use @autoreleasepool in main.m instead of NSAutoreleasePool?

I've noticed that there is a different way in Xcode 4.2 to start the main function:

int main(int argc, char *argv[])
{
    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil,
                                 NSStringFromClass([PlistAppDelegate class]));
    }
}

and

int main(int argc, char *argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    int retVal = UIApplicationMain(argc, argv, nil, nil);
    [pool release];
    return retVal;
}

Does anybody know the difference between those two?