The article makes it seem like it's 100% lock Samsung is going to make the Nexus again. But their source is the Digitimes article which is just rumor.
Maybe Google just loves AMOLED. Samsung controls like 95% of that market. If Google wants the cutting edge AMOLED, Samsung is the only one that can provide that. Samsung doesn't sell their best AMOLED to competitors. They keep that for themselves. They will however sell the previous gen AMOLED to competitors.
More likely it's because Samsung has complete control of everything in a smartphone except for the OS.