Nonsense. Hobbyist volumes are negligible. It's about volume markets like washing machines and other non space-constrained applications where single-layer PCBs are the norm, and there are other big, lumpy parts like relays which mean through-hole is more appropriate.
Any hobbyist-friendliness is just a spinoff from the requirements of real volume customers.
Well, it is not like theese machines are using anything else than 68000 or 8051. And to be honest I think it is never justified to use that paper one sided PCB. I know how much a 2-4 layer PCB costs in high volume, which can completely solve the design in SMD. And TH components are more expensive, a 1uF cap costs 6 cents instead of 0,4 in TH package. The population cost is 1 cent for SMD in contrast to a Chinese worker. 99% of the components are SMD, and they just dont make the good stuff in TH for good reasons.
I really dont know, how they justify their obsoleteness, and no-one seems to reveal the true story. I'm guessing that they calculate the cost of throwing out equipment, or they decided to use something for 20 years, and they are stuck with it. Accounting cannot handle it maybe.
Also, you should not bring up Arduino as an example for a good project. It was a student project, never intended to be used this broad.
http://www.adafruit.com/blog/2010/03/18/the-first-arduino-ever-made/They have a market aim. 0,5mm BGA is obviously hand held market, while QFP packages are for general. DIP is only justified for millitary/space/harsh.
And it is really not like you need to do so much old school prototyping with ARM. Pinouts and firmware is compatible (usually for a single company) so just buy one of the demoboards for a price of a pizza, and use that.