Well, when we went out west last Jan we were in a hurry so we traveled on the Flying J plan, which meant I had to deal with winey women cause wife wanted to put out slides and such (I am flexable but as tight as they park rigs in a Flying-J I did not want slides knocked off by a passing seim which was not supposed to be in the RV lot to begin with)
But it worked out fairly well.
Coming back we paid for campgrounds since there was less hurry, this year it will likely be a mixed lot. Longest I've stayed in a Wall-mart lot is a few hours (Actually wife stayed in the lot,,, I dropped and headed to a nearby business where the RV would not fit well, actually it would fit on the lot (They have several simular size rigs there) but I don't care for the traffic there with the RV so I parked and drove the towed) I don't like Wal-Mart for other reasons.
As for taking up employee parking... Many stores request emp;loyees park "Out around the edges" of the lot, in the less desierable parking places. It fits 100% with the Wal-Mart management style to demand (not request but demand) this of their employees. (This has to do with why I don't like Wall-mart) and, of course, as a courtisy to the customers and, thus to management, this is where I'm going to want to park my big rig, out along the edge, where nobody else is parked, so I'm not taking up prime parking
So, perhaps you were parked in the employee section of the lot