There's also the "time management" argument, which kind of complements ldcdc's statement above. Even when someone's proficient in a thing, they may still choose to have it done by someone else.
A friend of mine is a very good cook, yet she hires a personal chef to cook most of her meals. She's an obstetrician, spends a lot of time on call (and thus, out), and just doesn't have time to relax, do laundry, take care of her garden, cook, clean...and do her job. She hires out the bulk of the day-to-day cooking and cleaning, has a landscaping service come in twice a year for a "seasonal overhaul" of the lawn and garden, and thus leaves herself time to relax each day after work. She'll occasionally bake, cook a special meal for friends or a gathering, and do her "spring cleaning"; but she hires out the daily-maintenance stuff.
She's an amazing cook. She just chooses to spend her daily non-work time doing things other than cooking.
Web hosting (namely server management) is the same way with many people, and it likely always will be.
Lesli Schauf, TLM Network
Linux and Windows Shared Hosting since 2002: Scribehost