Some of the smaller or independent guys probably have their own 7700k for personal use but can't afford or get access to a 6900k just for the sake of being able to benchmark a product that few people will actually buy. Also, from other reviews, we've seen that the Intel 6, 8, and 10 core CPUs typically don't do any better than the 7700k so it's good enough. Add in that the 1700X is close in price and you have a pretty good reason to compare them for that reason alone. A 1700 is even cheaper and probably some of the best value you can get if you want an 8 core rig and have no qualms about overclocking. Maybe the R5 chips change that value proposition, but if all you care about is the best possible gaming CPU without concerns related to streaming, etc. then you have to compare it to the 7700k anyhow as that's the previous/current performance king.
Yes, but this is a bit out of the context. Recent discussion was that Nvidia driver doesn't work that well under DX12 (especially on ryzen). If you make test between I7-7700k and Ryzen, you are testing driver stack in different conditions (8 fast threads versus 16 slower threads). Same with crossfire vs single card tests, where you run different codepath alltogether under multigpu (and not even mentioning adding extra thread for 2nd video card).