> It's a lot harder to grow a consulting business beyond 30 to 40 hours a week because a human can only sell so much of his time.

Good consultants sells access to their knowledge, not their time. A consultant who's selling their time is not going to go far, for two reasons:

1 - You can't sell more time than you have (as you mentioned).

2 - Selling time means billing time (hourly or daily). That means the cost of your services will be compared against other hourly work, like design, data entry, and legal services. That comparison never works out in your favor.