As a relatively recent convert to Brompton, I think the prejudice against not only them, but the buyers of them, is not justified. To suggest that they're the first and only consideration for most people is ludicrous.
Cost:
Yes it's expensive, but compared to what? I've looked at virtually every other brand and discounted them for one reason or another. And one of the reasons was cost - certainly brands like Airminal (not a great fold either), Birdy and Oribike are more expensive or are on par.
Small wheel v big wheel:
For the record, the Brompton is my fourth folding bike as I didn't really want to get a 'small wheeled' bike. I had three full size folders - two Dahons and one Dahon clone. While I never had any problems with the legality of taking any of the three full size ones on the my train (Chiltern Railways) I did occasionally have to miss a train as there simply wasn't room to get on with the full size bike - fine if you were there first.
The actual fold:
We have two cars and I have to drive to the station in the mornings as I need to drop my daughter off at the child minders before parking the car up and riding to the station. The full-size ones would only go in the back of the estate car, not our convertible Mini. So whenever my wife needed the big car, I had to not cycle. This cost me about an extra £10 per day due to parking costs and tube fares and I'd rather ride anyway.
Looks:
I liked the look of the full-size bikes as they looked like a 'normal' bike. Initially I discounted Bromptons, because every one I saw was in BRG, with a brown leather brooks saddle, too upright, and normally had someone pootling along on it at about 8 mph. But I thought I'd better investigate some small wheeled folders and I did test ride a Dahon 8-speed small wheel folder back in 2008 before I got my first folder, and it was not solid at all. Compare that to this year and my first ride on the Brompton and I was surprised at how soild it felt. I also think that without the M bars, they look a bit better, although mine is wearing short risers bars due to the S being just a little bit too low. The new range of colours helps.
The ride:
Whoever said they're slow, or that Brommie riders aren't interested in performance is sadly mistaken. I've ridden 6 bikes on my normal commute now. A cheapo B'Twin Triban 3 road bike, a rabbit.de 26" folder, a Dahon Matrix 2008 with the big hinge, a Dahon Matrix 2009 with the lockjaw system, an M3L hired Brompton and my current H6L Brompton. I use Strava and my current Brommie is second only to the road bike on certain sections and only seconds off the pace of the Dahons on others. It's really not a slow machine. I've topped mine out at 44.4mph on a downhill section, and it sits quite happily at about 18mph on the flat. over 11.5 miles on my commute, I average about 15.5mph which is exactly the same as the Dahon and is more down to traffic lights and traffic than anything else.
Overall, it's the bike I should have bought years ago. I can use it every day, regardless of which car I'm in, it fits on the train properly and it is future proof (Chiltern were going to introduce a two-fold only rule for folders meaning anything with a single hinge would then become not strictly legal).
