I agree that this way of displaying the data is appropriate, but it would be nice to have a very visible indicator of this. Some kind of highlighted “fold” line or something at the very bottom of the chart, maybe. If I can deduce the units from context, and the trend is more interesting than absolute numbers, then I’m not going to look at the axes most of the time
It’s about setting expectations. The wording is chosen because they believe that paying open source developers for their work should be the norm, not the exception. Calling it a donation would not do that justice. Their wording is saying “Here’s the software, we’ll trust you to pay us for it if it brings you value and you can afford it”. It’s an explicit expectation to pay, unless you have good reasons not to, which is also fine but should be the exception. Whereas a donation is very much optional and not the default expectation by nature.
In the end it’s just a semantic difference, it’s just all about making expectations clear even if there is no enforcement around them.