Stop, don't promote your best Sale's Person!

Why is it that we expect our best sales performers "to know" how to manage? They socialize in the pub Friday after a hard week travelling and selling, and, on Monday am. relationships change because now "he/she" is the manager. When we promote our best sale's people into sales manager it is not without risk. The skill set required is very different.
There is training and support available but very often it is never utilized or indeed called upon. Hard be it for the new manager to ask for help for it highlights a weakness - or so the perception goes. I disagree. Asking for support in the early days is a strength which will help support and develop the good work already done by that person in reaching this promotion. Am I right or wrong?
www.ktaluk.com - KTALCoach (Twitter)