Very much depends on your use scenario. Does the texel being evaluated through your pixel shader only reference a single texture for it's computation? If your making a game that only needs simple texturing, and to have it sampled by a single SamplerState at any given shader execution, sure one Texture2D, and SamplerState should be fine.
As MJP stated, you'll change the texture, and sampler bindslots cpu side for different textures, and (if need be) corresponding samplers, and the bindslots will retain there textures, and samplers between draw calls, and shader swaps.
The website you mentioned will eventually step you through more advanced use scenarios where for a given texel you'll evaluate it against several textures, such as, normal maps, shadow maps, and ect.