I'd say that is correct. In a sense it's like part availability for cars or washing machines, and is similarly quite an outrageous situation too: around here law mandates 10y of parts availability; trouble is, reliability has progressively improved to the point that this becomes ludicrously insufficient.

An example: I bought a car five years ago, it's well tended and shows no sign of being anywhere close to the scrape yard five years from now, yet parts will become hard to come by; case in point my other car is turning 16 (sixteen!) and barring the need for a full body paint job because the varnish is gradually peeling away (which is kinda expected), is equally in such good order as to most probably be in similar condition for another 10-15 years with proper maintenance; but will I be able to? Parts are getting rarer as they've been in a stock-remainder only basis for five years.

Another example: my washing machine had a part fail at the 7 year mark. Fine, parts are supposed to be available, so just repair? Well, the part moved out of production to stock-basis because they evaluated statistically that they have enough stock to cover the 10y mark. Problem: the stock is a sort of archival with glacial operation speeds, the time quoted for part shipping was shy of 6 months, and I couldn't find a replacement. So I bought a new machine out of sheer necessity.

10y is way too short for parts. Software, notably OS and its compatibility primitives for third party software, should be counted as parts. 7y for software is better than before but still way too short.

> Desktop OSes tend to support hardware for much longer than mobile OSes.

I feel like this is increasingly less true, at least to the point that the difference becomes immaterial to the problem.