Whether open source is a use-case or an ideology really depends on the requirements of the individual or organization. Some work in a world where security auditing of all source code is required, or source code is required to maintain compatibility, but of course, others are free from these restrictions and are willing to closed source binaries.

If you're under no requirement restrictions, then calling the insistence on open source code an ideology or preference is entirely fair.

If your only goal is to just play as many different games as possible, then using linux is a bad choice from the start, and you're obviously intending on running closed source code, so requirements and preferences make no difference to you.

If you hope to run as much open source as possible, then buying hardware from friendly vendors is your best bet. Your choices for both modern and supported graphics hardware with open source support are pretty much limited to Intel and AMD/ATI.

Intel HD4000 graphics integrated with some of their CPUs. The only major driver is open source, and Intel has been working with Valve to fix issues in their game ports to Linux.

However, to put it gently, the performance is not close to on-par with current generation Nvidia and AMD offerings.