If I download an Ubuntu Server ISO, I get my download immediately, but the page has a nice prompt to register for a whitepaper to get the most out of my new server product.
If I download the Ubuntu Desktop ISO, I still get my download immediately, but additionally I see some nice prompts about donating to support their operations.
Everything about both flows inspires trust that they aren't trying to withhold my download for the sake of selling consulting services or soliciting donations.