Most of the data is free and access costs no money. Some of it is even free across all of Europe due to open governmental data regulations.
Some detailed or highly localised data would probably only be available commercially. But satellite data for example can be downloaded realtime by anyone.
If WetterOnline was paying for their weather data then they didn't get their data from DWD.
The DWD data is completely free. You don't even need a registration or API key or something like that. I just tried and downloaded Radar images. I can't read that format, but I could download it.
The issue is that the legal mandate of DWD is just to provide the data and not to compete with private companies. It probably made sense when those laws where written, but now it is just stupid.
The problem with such a non-compete law is that your public service doesn't really need to change much over time, but a commercial business might figure out a way to make money off of it and suddenly the private side changed forcing the public side to shut down or something like that and now everyone that was building on top of that public stuff gets screwed over. The side-effects are so big, it's hard to capture in a law.
> private side changed forcing the public side to shut down or something
As far as I am aware they are purely funded by Taxes, so I can't imagine any way that these private companies could change to force the public service to close.
Well, say a weather data service is provided by the government but is only allowed to operate as long as they don't compete with a commercial service. At that time there is no commercial service so it's fine.
10 years later a commercial service is started and now the public service has to change because that's what the law says. The public service didn't do anything wrong and didn't change anything, but because something in the private space changed the public space now has to stop providing a service. That's what I meant by change in the weather data example.
This law was written in 2015, so no, it didn't make more sense then. (the concept certainly is older, but while writing the 2015 law it was specifically modified to add this restriction again)
Some detailed or highly localised data would probably only be available commercially. But satellite data for example can be downloaded realtime by anyone.