I would reserve the idea of "attentional High Fructose Corn Sugar' for just some specific user-experiences, rather than the internet as a whole.

There are some interface patterns that tend to heighten the sense of importance/urgency/novelty... without any real substance. Those help create the overstimulation-crash-craving cycle like dietary sugar binges.

The interleaved Twitter/Facebook streams are one form of attentional sugar. But the HN format is, too: mixed topics, jittery time-influenced rankings, random arrival of comments/karma-deltas.