Perhaps I'm reading too much into it & that "high power gaming systems" is relative when comparing different types of systems.
Note that 12V2 only supplies the AUX12V (2x12V) 4-pin plug, which feeds only the CPU. 12V1 supplies 12V to all the other components that require it. This can lead to a problem with high power gaming systems that utilize two high power video cards in SLI or Crossfire mode.
Personally, I get the impression this says it's likely to be a problem, almost to the point that it will happen. In a way it's pretty much saying to me, Antec's SLI certified PSU is likely to fail in the type of setup it's certified for.
Now what I mean by clarification is perhaps the word "can" can be substituted with the word "might" or something of that nature. And that the word "can" makes it out to be a bit misleading.
Truth be told, I haven't heard many or if at all any power lacking related stories between SLI certified PSUs w/ two 12V lines & systems built around SLI or similar to suggest a high likelihood to failure. At least for the present time being.
Perhaps I'm asking too much and if so, then I apologize for suggesting to make a very detailed and informative PSU article a bit clearer.