The major thing that put John Carmack at the top of his field, even more than his extreme intelligence, was his unrelenting grindset. He would work days and nights, often taking a weekend and locking himself in a hotel room, to solve a problem. He has said in interviews that unless you work those 12+ hour days you just aren't going to write world-class software.

If you really want to develop on the cutting edge, you need a lot more than smarts. You have to have that dog in you. That fire in your belly that makes you obsessed, consumed with your work and solving the problems you set out to solve. If you don't... you're gonna lose out to someone who does. Go sling Java for a bank or insurance company, then, if you want to punch out at 5.

Scott Wu has that dog in him. It's reasonable for him to expect the same of his employees.