I'm sorry, I don't understand your point.
If you invest that $38K then you will have $33M after 100 years time.
If you paid that $38K to Wordpress then you won't see a cent of that money back.
I don't see how it makes financial sense to give $38K to Wordpress rather than investing it yourself and paying monthly hosting fees.
You're paying for the security / peace of mind, and I'm sure you can picture some people preferring to do that than to self-manage hosting content (and updating technology over time) for 100 years.
Edit: Having said that, I don't think Wordpress is the right fit for this. I think it should've been a separate company, with a separate brand and a separate legal structure that enforced keeping things up for 100 years and enforced using the investment profits to keep the content up and maintain the infrastructure even as technology changed.
It seems like the best way to guarantee that something runs for 100 years, actually; build an investment fund whose mandate is to keep some basic websites up on a couple cheap servers.
Edit: Even if technology changes, that's just a maintenance job every year - keeping the underlying infrastructure updated. Some years it will be cheap, some years it'll be a bit more costly, but ultimately it's not impossible at all, especially if they've got a big number of clients (and thus a big fund to draw from).