This is the same as saying there are a few more complaints on Shimano gear compared to Campagnolo just because they simply build better shifters? When Shimano sells a lot more than Campy, 1 or 2% of that complaint magnifies significantly for Shimano or Dahon!

Brompton and Dahon make good bikes. When I was buying my Dahon Mu SL, I was contemplating either Brompton or Dahon. I chose Dahon because it fits my riding requirements; being able to fit Big Apples, a new Capreo rear second wheel for faster club rides, light touring with Dahon racks etc plus adding a 2x9 (18 speeds) with little money. Perhaps you can do that with the Brompton (adding more bigger gear inches for less money than 1 extra 55T chain ring and a Capreo 9-26? with my Mu SL) or Big Apple? And my local Brompton dealers here in Vancouver do not seem interested in selling me Bromptons that I can heavily mod. One told me to buy Dahon. The other; well closed down his business and re-open with a new name while ignoring my Groupon (seemed to be operating a shady business) --that Groupon refunded me the full amount was thankful.

Speaking of special parts supply. Bikes have proprietary and sometimes OEM parts bolted on.
Some individuals here try to convince you that both are the same. This is totally incorrect. A proprietary part is something you can not buy in an open market. In that case, the bike maker has to provide replacement parts to the customer, though this is not almost the case even with the most famous and popular bike brands either! This includes rear dérailleur hanger, folding hinges and posts and a few speciality wheels with special hubs and spokes that can not be readily or easily obtained. Brompton bikes have quite a bit more proprietary parts than Dahon bikes, so it is not uncommon for them to have parts. Well they should.
OEM parts are basically parts that are made specifically for the bike to match its design,lines,colors etc.. However, these parts are available as generic components on the open market, just not with the same colors, design or lines etc. When these OEM parts wear out, most bike makers expect that you will be replacing with better name brand parts. The common practice is to include cheap bottom bracket, headset and wheel hubs or colorful tires and ergo shifters. Most bike makers do not stock OEM parts. If they do, those are usually extras. Bike makers order enough parts to make enough bikes. If you INSIST in ordering OEM parts in the attempt to restore a bike to its original condition, this usually involves research time and more costly parts as they can be rare.