However the answer to any question around why something is expensive or not is economics, specifically supply and demand, marketing and distribution channels, and barriers to entry.
This is the technology sector. We have made a cottage industry out of taking things that used to be at the maximum level of complexity and turning them into household items. You could write a similar article about how web servers work -- there's an amazing amount of complexity in there, but we've commoditized all of it. Ultrasound tech will follow the same trajectory, although I have no idea how long that will take. In addition, ultrasound providers are marketing towards large, rich, healtchare providers who are operating in a tightly-regulated market. If I had a $1,000 ultrasound that only worked for a year, was quirky, might scald me or my patient, but was good for quick diangoses in the field in third-world countries? It might be all I would need. There is no universal "ultrasound" device that has to meet a ton of specs. That's just the way the market is configured currently.
Good article. Lots of cool stuff in there.