Great news, Heathrow Airport has finally caught up with the late 20th century, and started supporting train ticket collection! (You used to have to argue with them, board a train to London with only the booking confirmation email, argue with the conductor, then collect tickets in Paddington) For T2/T3, head into the station past the roving ticket sellers, walk to the purple Heathrow Express ticket machines, then almost behind you tucked away on the other wall are 4 other ticket machines. Two are collection only ones, which ask for a credit card (Nectar cards often work too...), then prompt for the booking reference and finally print tickets. I think the other two might be full ticket machines, but I didn't have time to check. I gather there's something similar in T5 as well, it'd be great if someone could snap some photos next time they're there, assuming they're not in a hurry as I was today!
Was the complication due to the fact that strictly speaking the Heathrow stations have nothing to do with the rest of the rail system?
You've always been able to buy tickets to/from any station and Heathrow, so from that perspective it's a normal part of the system. You just couldn't buy those from Heathrow, they used to insist on only selling tickets for the HEX and stations on the Heathrow Connect route, presumably so they could keep all the money. It was a policy thing, but I think the private bit of track let them largely get away with it Not sure if it's due to complaints, or Crossrail, or something else, but it's now starting to act more like a regular station (though not completely)