Seppi had his results for the very fact that he is passive and very 'tidy/neat' in his game style which is poison for players like Verdasco and Paire. As for the two sets against Djokovic, I think everyone in here agrees on the fact that DJ never looked in trouble and went down mainly beacuse he was missing a lot of shots. Other slams he went out R1 to Gasquet in four sets, R1 Istomin 5 sets (he could have won) and R1 to Robredo in straights sets (...). Not so much impressive if u ask me.
As for Monfils we are saying the same thing, he should have ballbashed since he was quite tired. otherwise running 10km in every point doesn't help at all.
You could say Seppi was a passive player a couple of years ago, but I would say that's one aspect of his game which he has improved a lot and one of the reasons why he started to get better results. His serve overall improved a lot (gets a lot of free points with 1st, 2nd is not as vulnerable) and he's actually going for winners a lot more than before. Replace passive for patient and you've got a much more accurate description of how he plays, he's not going to hit through players and overpower them consistently but, instead, he's pretty good at constructing points and flattening his shots at right times.