Less literally, life is worth living because we all have a lifetime to experience pleasure and happiness, no one denies that happiness is an unworthy goal. If someone has no hope of future happiness, and is right (certain medical conditions, daily suffering.. not "my girlfriend broke up with me") than life might not have "meaning" for them.
The second quote still doesn't really hit the nail on the head, although it seems closer. I think it just begs the question: what is the purpose of my happiness? Does it really matter?
The third quote forces me to define what meaning is. I think of it as just "mattering." Does anything really matter? Do my actions ultimately matter? Does my happiness matter, or my existence? I think that if you take an honest look at the universe, it looks like (a) we are a very very small portion of it, something that almost looks like an "accident" and (b) events in the universe are dictated by its physical laws. It's a giant machine that's automatically running but doesn't seem to have anywhere specific it's trying to get to because no one is guiding it there. (Sorry fundies, you lose.) If there is no final goal, then no single event can objectively matter. It's the difference between playing a tennis match and just volleying. Volleying has no winner or loser, so each hit or miss doesn't matter. It can matter to you personally, subjectively, if you invent your own goal (e.g., hit 5 in a row) but ultimately, objectively, it's meaningless.