In the case of RackSpace, they hire real sysadmins. This means they pay much better money compared to, for example, a cable company. When you pay a higher salary, you have a better pool of candidates to pick one.
In the case of both companies, they make a product that people are passionate about, and they in-source tech support. If you are a pure tech support company, you have a real challenge there. You have to hire people passionate about whatever you are supporting. That might be hard if you get a contract with a company that has a really bad corporate culture, or isn't willing to make your employees love their products.
For example, lets say you were supporting SIP phones from a SIP integrator. If the engineers doing the installs and onsite maintenance are caustic people, that's going to rub off on your employees. Since you're only building the tech support aspect of someone else s company, you can't build a great holistic company culture around the product or service you support.