I think Tim was suffering a bit during his match today. Nevertheless, he IS and often in his career HAS been a markedly very inconsistent player. Like this week: he plays fantastically well against Massu, and then, against Chela, he plays one of the worst defensive games of the tournament so far.
Henman's is much the same story as Nalbandian's. He has the skills, but not the consistency to see himself through.