Hope this doesn't get buried, but there's a lot of misinformation in this thread mixed with some good stuff.

Hawking likely doesn't have ALS, and he certainly does NOT have what we classically think of ALS. What you're seeing is the problem inherent in all criteria based diagnoses.

Simply put, ALS is diagnosed when we see signs of upper motor neuron disease (increased reflexes, increased tone, etc)) and signs of lower motor neuron disease (decreased reflexes, fasciculations...which are those tiny twitches in muscles that are very common in people, etc.). The symptoms need to progress over time, AND there cannot be a better explanation for the symptoms. ALS can be broken down into possible, probably, or definite ALS based on criteria and in how many places in the body the symptoms are showing.

The problem is that many diseases can cause those upper and/or lower motor neuron symptoms, so it takes a CAREFUL and thorough history and examination with an appropriate panel of tests to make the diagnosis. Even then, the best neurologists have a chance of missing something out there, especially things that are more rare than ALS. This carries a small but not entirely absent chance of mislabeling somebody as ALS.

Doctors are people as well, and they're only as good as their fund of knowledge (or ability to use the resources out there effectively to expand their fund of knowledge when needed). If they're never heard of a disease, the likelihood that they'll diagnose that disease is pretty damn small, obviously. When it comes to mimics of ALS, the diseases out there are often very rare - spinal muscular atrophy, progressive muscular atrophy, primary lateral sclerosis...these are all things that most people have never heard of and can look a bit like ALS. Then there are common things that can give symptoms of motor neuron disease and confound the diagnosis - hell, a bad neck can do this.

And to my original point - if you have a disease like ALS that is diagnosed based on criteria, a lot of these diseases in the right context may make somebody meet that criteria, a label of ALS is placed, and it sticks. Taking a diagnosis from somebody is harder than you might think too. People who are misdiagnosed with diseases often have incorporated the disease into their identity - they're online in groups, they are part of organizations for the disease, they have believed a prognosis for a long time, and they don't give that up as easily as you'd hope somebody would.

Back to Hawking - even if he fully meets criteria for ALS, his disease does not fit close to the typical course of ALS. Therefore, it would be more reasonable to conclude that he does NOT have ALS but rather he has an "ALS-like disease that we don't have a name for yet". So you don't have to go down any conspiracy route, and you don't have to ask yourself what his case means for all people with ALS or how people with a lot of money and resources would do with ALS, or whatever erroneous conclusions we want to make from his case that is probably just a mislabeling anyway - he's different, period.

The better lesson here is to be skeptical of criteria based diseases - remember that criteria only gets you a certain amount of sensitivity and specificity in detecting and confirming disease. Headaches (migraine in particular), fibromyalgia, TIAs, and psych disorders are some great examples of criteria based diagnoses that need looked at long and hard and with a healthy respect to the Dunning-Kruger effect.

Source - I'm a neurologist who is in charge of teaching a Neurology department at a major university on a throw away account (disclaimer - its 4 am and I woke up for no good reason so if anything I wrote here sounds stupid, I'm blaming that).

For what its worth I kept somebody from an ALS diagnosis just last week after looking back many years into his history and seeing that he had radiation to the neck that would completely explain his symptoms.