There are two approaches to hiring (http://www.bhorowitz.com/hiring_executives_if_you_ve_never_done_the_job_how_do_you_hire_somebody_good) — hiring for strength and hiring for lack of weaknesses. If you always hire just people with lack of weaknesses you get great execution and lots of iterative refinement, but very few revolutions. If you always hire just people with strengths, you get constant revolutions but nothing really done. So you need both in order to have a successful organization. Committees are great at discovering weaknesses and very bad at hiring for strength. Therefore you need strong people heading your organization who are self-confident enough to hire for strength every now and then and disregard opinion of the committee.
Engineers are mostly hired for their execution abilities. Therefore hiring committees make perfect sense. But every now and then you need a Jack Dorsey-type of engineer to shake things up and that’s a call a CEO/CTO should make.