And yet as a low LP PLAT, I was upgraded well in advance of departure (not quite D-48 but close to D-48) on a PHX-DFW flight.
On that same itinerary, I did not clear on STS-PHX. On an E75 with its very generous F:Y ratio. (But I did wind up with an empty seat next to me in MCE, exactly as I predicted I would.)
There's massive risk in drawing too many conclusions from anecdotes. A PLAT can wind up upgraded on a hub-hub flight.