If upvoting a post/comment (which gives the author karma points) would risk triggering its deletion (by making the author cross the karma threshold), then is that not effectively turning the karma system on its head?
Under such a system, if I think a post is valuable, I would then try to "protect" it and its author's account by downvoting it. Similarly, if I think a post is not valuable, I can help trigger its eventual deletion by upvoting it.
That would only really matter if the poster were really close to the threshold. Moreover the gaming of the system would be unlikely to work forever, requiring too much coordination of effort.
But to answer your question, yes, it is turning the karma system on its head for people near the top of the standings; the idea being that having "titans of karma" in the community becomes detrimental at some point.
Under such a system, if I think a post is valuable, I would then try to "protect" it and its author's account by downvoting it. Similarly, if I think a post is not valuable, I can help trigger its eventual deletion by upvoting it.