True, it has given other players (especially those 3 you mention) a slightly better mathematical chance of qualifying, but, realistically, they are still a long way off when you consider that JMDP is likely to raise the bar to at least 330pts (and, working with Ferrer and Roddick, this could go beyond 350pts imo).
Yes, they all made the finals of their respective tournaments and now they need to win the titles to have a fighting chance.
As for ferrer and del potro. ferrer could be facing lopez, who knock him out in the first round last year at madrid. del potro could have another master cup hopeful take him out in nalbandian or berdych.
So both ferrer and del potro haven't guarantee themselves in qualifying for the master cup yet.
Anyways, i think their could be lot of surprised this week, noone expected kiefer, wawrinka or mardy fish to make a master final this year. So their still possibility another player that still has mathematically chance to qualify for the master cup could making the final in madrid.