I was told by a couple of dealers that only Runco's cinewide uses all the available pixels from a native 2.35:1 format where other projectors using an anamorphic lens just stretch the 1.85:1 image to 2.35:1 and you lose pixels that way. Is this true??

No - Runco packages things nicely so it works "out of the box", but does it the same way everyone else does, with a video processor and anamorphic lens - since the source has the "bars" (HD/BlueRay formats don't have anamorphic support, so the bars are in the media), it needs to be stretched to use all the panel.

http://www.runco.com/cinewide.html

Just to say it outright, there are currently no 2.35 native panels that any consumer could buy.

Everyone, who uses all the pixels, stretches the image with a processor and uses a lens of some sort (squeeze one way or stretch the other) to get the AR to 2.35.