I'm not surprised, not at all. The A320 ELAC uses 3 68k chips, and the A320 SEC uses an 80186 and even an 8086 chip. Why? For lots of reasons. Basically, it doesn't require billions of instructions per second, it doesn't need to access gigabytes of memory, and most importantly, they are proven chips that have gone through years of testing, and they are relatively simple. At the time they were complicated, granted, but they were still within reach of severe quality control. Remember the problems Intel had with the Pentium and floating point calculations? Nothing serious, but still... The chip was so complex that problems crept into the design phase, and at 38000 feet, you do not want problems. To cite a fellow Slashdotter above, (thanks tekrat), Critical systems require reliable, proven, hardened hardware, not flakey netbooks. Enough design faults have crept into aeronautical design, so I can only imagine the space sector. NASA used to program everything in 68k because they were reliable, simple, fast enough, and because they had lots of really, really good engineers that knew every single aspect of the chips.
Don't get me wrong, I love todays chips, and i7s look sexy, but with a TDP of 130W for the Extreme Edition chips, they just add problems. Running at 3.2GHz, with over a billion transistors, you are just asking for trouble. At those speeds and heat, problems do happen, the system will crash. Ok, not often, but with mission critical systems, just once is enough.
Did anyone seriously expect the shuttle to run quad-cores with terabytes of RAM?