Actually I am quite new to tennis and I have seen Karlovic play only once 20 minutes. But there must be a big difference between the 1st and 2nd serve, because he only wins half of his second serves and almost all of his first serves (86% by far the best percentage of every player, as well most aces).
Not really. With his 1st serve he goes for the corners and wants aces. His
2nd serve isnt much weaker but he usually puts it in the middle of the box and it is easily returnable.