Earlier quoted context omitted.
That assumes they have control over the DNS. Sounds like they don't with many end customers.
They shouldn't be giving their customers a static IP, they should be giving them a 'customername.ourplatform.com' address that the customer can point a CNAME at.
This was addressed in the article: There is a tendency within that industry of whitelisting API access etc. by source IP, so their customers do need static IPs not primarily for inbound traffic, but to be able to access the APIs they need.
Now it's still stupid of them to not abstract that away from the individual customer servers but, but this issue isn't solved with cname's.