This session at ISPCON in Orlando describes the ongoing debate: "Who Will Win? Hosting vs. Owned, Marketers vs. Infrastructure Providers". ISP owners like to do everything in house. Build it themselves. More control. Doug McDonald used to tell ISPCON attendees: "If you can't build it faster, cheaper and better, then buy it." It still holds true. While some clients are happy to outsource some services, others are not.
When you have a small business with 10 or less employees, how many experts do you think you have? And in how many areas? Most clients like to tell me about the Boy Wonder who works for them, who can do anything. Yeah, but what if he wants a life? Or the flip-side is the Red Bus scenario: What if he gets hit by a bus?
I'm not saying outsource the critical things, but some of the less critical can certainly be safely outsourced and may even add margin (if you count time, energy and effort as time). Loral Langmeier tells her clients to get a maid - it gives you back some time. And time is money.
One last point: usually the strategic partner that provides you the platform has a team that keeps that one platform running. How many people do you have keeping that same platform running?