I agree. A great way to solve that problem is with retractable casters that allow the legs to carry weight while you're using the table (or whatever), yet allow you to move it around readily. Looking to add these to my table saw (cast iron table, it's more than slightly a pain to move around when that needs to happen).
"good castors aren’t cheap and cheap castors aren’t good". Indeed. I bought some castors from a big box home improvement center, and the brake was marked backwards. When you pressed 'unlock', it actually locked. My wife damaged our new kitchen floors, and the big box store ending up paying for the floor to be ripped up and redone.
"keep the thing from not moving". Sort of an odd-ball double negative. What you really meant was "keep the thing from moving" or "ensure the thing does not move".
Another handy device for carts/tables on wheels especially if you don't have locks on the casters is a floor lock for carts. A google search will give you some pics.