Only a short time ago, planning a trip without a travel agent would be crazy. Travel agents allow the vacationer(s) to focus solely on the vacation, rather than on tasks which they're not particularly suited to, like organizing international, multi-leg flights, getting deals on hotels, and finding fun things to do once they get there.
In... The Age of the Internet... the networking ability of a music industry studio is less useful. The equipment is much cheaper, and the techniques are more accessible, so you can have cross country collaborations that produce music that sounds better than the Beyonce sound debacle.
The musician doesn't need to perform all of the roles himself, but it would help if he could choose the roles he needs without signing a 6 CD 3 pence a tour date contract.