"I have been working on several Europe runs and was very frustrated that although I could price decent routings ORD-LON on Expedia.com or Thestoremaker.com, identical itineraries were consistently pricing 3x as much on AA.com or Travelocity.com for all the dates I tried. "

If expedia has good fares, why not just book through them?

"So Expedia and other sites are wrong in allowing me to book them on Sat. night stay required fares. Is this correct information?"

Surely it depends on the rules of the tickets that they are selling. I had a look on aa.com and checked out 31jan-1Feb and it quoted a fare of $517.70 (booked in L) whilst expedia quoted $532.60 (booked in N).

Dave