Here's one quote from the wikipedia article on AMOLED
"Current demand for AMOLED screens is high and, due to supply shortages of the Samsung-produced displays, certain models of HTC smartphones have been changed to use "Sony's SLCD" displays in the future. Construction of new production facilities in 2011 will increase the production of AMOLED screens to cope with demand."
The S-LCD is a joint venture between them and Samsung, and manufactures these screens. Ultimately the significance of all this is that Sony is either no longer leading edge or no longer cost-effective enough to be viable for its own cutting-edge Vita.
All this says to me is that Samsung is the company of choice for both affordable and high-quality screens, so much so that for choice of screens Sony will pick Samsung's product over their own.
You guys aren't surprise, but this is definitely news to me. Up until now, I always thought Sony was top dog in this regard.