Oh man, I've been seeing this everywhere lately (not just cabinet hinges, but like, all sorts of home stuff). It's like people think bigger is always better, even when it's just plain unnecessary. You're totally right to notice it with those 3-inch hinges on a 30-inch door. I've got a buddy who builds furniture on the side and he swears some of these custom shops just use whatever hardware they have leftover from bigger jobs, so they don't have to order the right size. It's the same pattern I see with light fixtures, people put a giant chandelier over a tiny dining table or a huge faucet on a little bathroom sink. We're just surrounded by overkill, I guess. Makes you wonder if they care about the look or just getting the job done fast.