simply speaking - just rumors, no truth in that.
i don't know about before, right now intel cpus work well with both amd and nvidia gfx cards. amd cards need more cpu power than nvidia cards, so gfx card performance is more pronounced with intel cpu with amd gfx card. most amd cpus hold back the gfx cards in cpu-intensive situations. overclocking helps, but not up to the level of performance of stock intel cpu and amd gfx card combo. however, if you cherry-pick your amd and intel cpu, you can champion one amd cpu vs another intel cpu and vice versa. this link should give you an idea:http://www.tomshardware.com/reviews/gaming-fx-pentium-apu-benchmark,3120.html
it measures cpu performance against the strongest amd single gpu card. the overclocked i5 2500k is used as a scale to how other cpus perform.
cpu performance becomes even more pronounced if you have a multi-gpu combination running e.g. cfx, sli. both cfx and sli need good amount of cpu power. in those cases, an intel cpu would outperform a comparable amd cpu.http://www.tomshardware.com/reviews/fx-overclock-crossfire-ssd,3098.htmlhttp://www.tomshardware.com/reviews/core-i5-fx-6100-overclock-benchmark,3099.html
amd does advertise their combination of amd cpu, amd gfx card etc (may be motherboard chipsets, ram and cooler too) as a single platform - scorpius (iirc phenom + amd gfx card platform was called dragon?), but it's just a marketing gimmick. as long as you pick your parts for performance you don't have to stick with one single brand.