Isn't their fear that these smart employees can steal ideas from office or get client details and then start their own companies? What is your view regarding this?
Of all the reasons for one not to employ someone that is supposedly smarter than himself or herself, this is one that shouldn't bother you as it seems very selfish. It makes you more of an employer of labour that isn't in support of his or her employees self development. That's not okay as it would build in your staff the need to be dubious.
Employing someone that is supposedly smarter than you is an added advantage to your establishment. At the very least, your sure of some professional service or job. They say "A graders work for C graders", let the brains work while, you manage the brains.