It's an excuse that is commonly given - but easily avoidable if you care enough about the ones that pay your salary by buying processors from your company.
And not only that, but they did much more than the average Joe and essentially pin-pointed the issue for them. So yeah, inexcusable it is.
That's just not true. Intel published the erratum in April: https://www3.intel.com/content/dam/www/public/us/en/document... - search for SKL150. It was also clearly noted in Debian's intel-microcode changelog on May 15: http://metadata.ftp-master.debian.org/changelogs/non-free/i/...
They absolutely should have followed up to the OCaml people's support ticket. But sloppy followup is an issue that every large project encounters.