Well, that's sure only half of the truth. About 90% of all mobos are used for pre-build systems form DELL, IBM, HP and all the others and will never be changed anyway. In fact there are a lot of facts, that force the change of sockets, like adding build-in graphics, build-in memory controllers with various number of channels. Even raising the front channel speed and power consumption needs a new socket. Did you know, that only half of the pins is used for data. The other half is power and ground. And that you need a ground lane/pin between two high frequency data lanes to keep them from interfering, because they are to close? You can find some white papers on the net about this problems.
If you don't want to change sockets very often, then stick with AMD.
Most people do not upgrade their CPUs very often. And most people do not simply swap out an old CPU for a new CPU. They tend to simply buy new PCs which would likely have a new socket anyway.
My current rig is over 4 years old right now. By the time I decide to upgrade to Haswell or Broadwell, I don't mind buying a new motherboard 'cause mine has just started to become slightly flaky, but also because of tech advancements on the motherboard.