Apparently others have done this as well:

"Building a Movement of Corporate Philanthropy

We want to change the world through inspiring early–stage corporate philanthropy. Pledge 1% is an easy way to leverage a portion of your future success to support nonprofits in your community. It’s a small commitment today that can make a huge impact tomorrow. The sooner you start, the easier it is–so join your fellow founders by making a pledge today!" [1]

In the list are companies like Atlassian, Salesforce, and Yelp.

The pledge is either 1% of equity, time, product, or profit.

[1] https://pledge1percent.org

This is not philanthropy, this is a company financially supporting the essential foundation upon which their product is built.

Methinks you are confusing altruism with philanthropy/charity.

Either way, it is more than that due to PostgreSQL's software license. Because of that, we all (potentially) benefit.

And it is a commitment. A (somewhat) stable source. More so if more companies commit to such a pledge.

What's the difference?

The investor expects a tangible direct benefit from the investment. A philanthropist expects only the benefit of humanity as a whole, and maybe her own good feelings; or if you are cynical, prestige.

Potentially Citus may be worth a lot, so this is in no way just a symbolic gesture. IMHO it could be the start of something very right happening more often. It was funded for 13M so far btw (crunchbase data).

Their last round was 9.5m, so I'd say their valuation was probably $50m (postmoney) at the time. That was 3 years ago though, so it has likely gone up quite a bit.