Money generates money. To fund something in perpetuity you need enough that the returns from investing it (taking into account tax, costs, inflation, etc) exceed the annual payment needed. This is not an infinite amount.
I haven't checked the figures but the article claims the foundation has $400 million cash and Wikipedia costs under $2 million per annum. There's no easy way of calculating the maximum annual sum that can be taken out in perpetuity from a well managed endowment but it's certainly a lot more than 0.5%.