I've always been paid for my articles, including one by IGP so no worries from my point of view I will continue to offer them as and when.
As for the WH Smith thing, I happen to know the publishers of another fairly niche market mag who have pulled it from WH Smith after being asked to pay for them to stock it!!!
Might I suggest to IGP that they offer it to as many truckstops with shops as they can think of. Certainly in TMWs early days I used to get it at BP truckstops who stocked it. Usually Penrith or Birtley.