I never understood the businessmodel, why should a company that earns money on selling hardware also ask money for the software, you would expect that if the software was free more companies/people would choose the hardware. Oh well.
Maybe it's because Xilinx paid $200 MILLION to create Vivado as a replacement to how ever much money they had in ISE. There's also more support for customers who have purchased the paid version and there is also access to Xilinx owned IP beyond what you might get with the WebPack versions.
But they are good enough to give away a WebPack version (or even the Design version of Vivado) which allows the hobbyists and students to use their devices. They're not interested in hobbyists, of course, but they are vitally interested in students. What students learn in school they bring to their employers later on.
I installed Quartus several years ago and then read the license. I had just agreed that they could cancel my license at any time in the future, leaving me hanging for any projects I might have designed. Sure, I could ignore the notice... The thing is, it reminded my of UCSD cancelling all licenses to UCSD Pascal when the school decided they weren't in the software business and sold the rights. A lot of business applications suddenly became non-compliant. So, no more Atmel... I understand they have revised the license but I haven't looked. Nor will I...
In terms of Xilinx, you will ultimately install both WebPack ISE 14.7 to support legacy chips and Vivado for the newer stuff. Xilinx did not make Vivado support legacy devices.
But it's still free even though limited in comparison to the paid versions. But it's still free...