Hyper Reading - What's harder?

In Hayes' article "How We Read: Close, Hyper, Machine", there is much discussion of two points that seem contradictory to me:

• subjects of studies have more trouble concentrating on texts with more hyperlinks than texts with fewer hyperlinks
• the habitual reading of text with hyperlinks degrades a person's ability to concentrate

Shouldn't this be the opposite? If it's harder to concentrate on text with links, and you're reading text with links all the time, shouldn't you get better at concentrating? Is there some mysterious threshold in the human brain that makes it impossible to grow past this? That says "ARG IT'S JUST TOO HARD I QUIT!"? I sincerely doubt it. The human brain is awesome, and makes awesome adaptations.