The multitasking founder is an interesting emerging trend - Jack Dorsey being the most prominent example, and Steve Jobs before him. If an effective founder is the rarest commodity, and their role at mid-to-large startups can be reduced to its most essential elements, it makes a lot of economic sense.
It's probably an anti-pattern. The only great example, Steve Jobs, took the CEO title at Pixar but my sense is that he played more of a Chairman's role there, he only really did the full CEO thing at Apple.
Even Jobs had to neglect huge portions of Apple itself to focus on developing new products like the iPhone.
I can think of multiple counter-examples as well. People who are trying to run multiple organizations and doing rather poorly (as judged by results). I wouldn't want to single them out publicly though. Besides, it's rather difficult to judge the cause and effect for things like this.
I agree that it is hard to focus on multiple things. Certainly I am not "running" Justin.tv/TwitchTV by any means: my cofounder Emmett Shear is in every sense of it. I don't think I could have a day to day operational role at two companies. At JTV/TTV I focus on providing value by advising those people who are in operational roles.
