I have to say I rather agree. I only got my Brompton this year. I'm really pleased with everything except Brompton's attitude to maintenance. I was really taken aback when I found that you can't buy and fit stems. Mine came a bit loose a while back, in the normal way of things; I tightened that myself, but maybe I should have taken that into a dealer too? There's not really much difference between that and fitting one.
It was bad enough finding that we aren't allowed to service the rear pivots. I've done that too, and it's not hard - but they won't sell the tools and they no longer sell the parts.
Bromptons are widely ridden by enthusiasts, many of whom do all their own maintenance on any bike. Are they trying to drive us away?