AMD is quite cost competitive against low and midrange Intel processors that have about the same performance, but Intel is more power efficient, which is a big deal for servers, especially heavily loaded ones. Small providers are doing good if they can get data center power for $20 an amp, which means that each watt going to the CPU costs about $2 a year. So if an AMD FX8350 (125W) computes about as well as an Intel E3-1230v2 (70 W), over a 3 year hardware lifecycle Intel saves you around $300 in power bills. Even if AMD gave you the FX8350 for free, you'd still be ahead paying retail for the E3.
For a home computer it's less of an issue: the computer is powered off or idling most of the time, so power consumption is much lower, and people are more sensitive to up-front expenditures than to monthly expenses.