I am afraid that I am one of those that do pay the outrageous £28 [in fact £56 as for some reason Mrs W wants to sit next to me], but only on the flight into the US [TPA to be precise] By being near the front of the cabin we are fairly sure to be at the front of the queue at immigration, and will only have a 20 minute wait rather than 60/70 minutes.
Personally, after an 8 hour flight, I am prepared to pay the extra, in order to get out of the airport as quickly as possible. Others will save their money and 'pay' with their time.
Inbound to the UK I will check in on-line and take my chances, as I will have to queue at LGW regardless of where I sit.