That's a pretty astute point. I can see them sharing the same database for both sites but displaying the CSS/HTML questions both on doctype and SO, but doctype

That's a pretty astute point. I can see them sharing the same database for both sites but displaying the CSS/HTML questions both on doctype and SO, but doctype restricted to CSS/HTML only. This will allow them to get content through multiple channels but allow them to sell more targeted ads on doctype.