Yea, the real world aspect, is if they are 'that' good, they will move onto either high priced consulting or higher level job which kind of moves away from the original question what is the most important skill. I don't think it's a skill, I think it's many skills. The most important think I think a DBA needs is the skill of Jack of All Trades, to be able to quickly deliver on a development project, turn around solve a production problem, spit out a report for management, and if something bad happens recover an environment. It's why DBAs are typically paid well. A good DBA is worth his weight in gold.