"Depressing but true": Agree. You're also right about the extra income from speaking engagements, etc.

The challenge is that only certain types of books can generate that income: for example, business and self-improvement books. Novelists and many others are expected to speak for free. Only those at the very top (including celebrities) can get accepted by speakers' bureaus that will help them earn big $$$.

Authors of children's books also get paid to speak at schools, which have a budget for that. And it's good money: I don't writer children's books, but I've made $500 for a one-hour talk to a school for speaking about writing generally.