1. How do these things differ? Said in this way, the phrase is a legitimate question that the speaker wants answered. What's the difference between these two recipes? They use the exact same ingredients and everything. What's the difference between all these cell phones?

2. What does it matter? Said in this way, the phrase is usually an aside highlighting the speaker's frustration. We can take the long way home, or we can sit in traffic here. Both ways will take forever, so what's the difference? What's the difference if I come home on Friday night or Saturday morning? You guys will be asleep either way!