I suspect you're right. Money isn't the issue here; it's luck of the draw.
My best friend's father died of ALS two years ago, and like your stepfather, he was very successful, wealthy, and motivated. He was also professionally and personally productive up until the last second. As I recall, his disease progressed like a step function whose "steps" were of indeterminate length. He'd lose some functionality, then remain relatively stable at that level for months on end, then suddenly wake up one morning substantially worse. The process repeated, and there was seemingly no rhyme or reason to the length of the intervals. At any given stage, his doctors said he could last for years, or maybe months, or maybe days, in that condition.
[Don't get me wrong; I am extremely glad that Dr. Hawking has survived as long as he has, and I hope that he continues to fight and win.]
Another vote for this. My mom died of ALS, diagnosed in November at age 75, died the following August. In retrospect she was showing symptoms maybe 12–18 months earlier but the early symptoms in her case were just a gradual decline in strength that we attributed to aging. Not that anything can really be done; there are one or two drugs that have a very minimal (but statistically measurable) benefit, but they are very expensive and while they may slightly extend your life (we are talking perhaps a month or two on average) they don't improve your function.
After her diagnosis she attended a few support group meetings, and it was striking at how the disease progressed differently in different people. One man had been diagnosed years earlier and was still able to do work around his farm and house, he seemed almost normal. Others were in wheelchairs and could barely talk, and had been normal only a year earlier.
I wouldn't call Hawking lucky as the disease is absolutely a terrible thing, but given that he has it, his remarkable longevity does seem to be on the lucky end of the statistical distribution.
My best friend's father died of ALS two years ago, and like your stepfather, he was very successful, wealthy, and motivated. He was also professionally and personally productive up until the last second. As I recall, his disease progressed like a step function whose "steps" were of indeterminate length. He'd lose some functionality, then remain relatively stable at that level for months on end, then suddenly wake up one morning substantially worse. The process repeated, and there was seemingly no rhyme or reason to the length of the intervals. At any given stage, his doctors said he could last for years, or maybe months, or maybe days, in that condition.
[Don't get me wrong; I am extremely glad that Dr. Hawking has survived as long as he has, and I hope that he continues to fight and win.]