The Schlecks have plenty more than 4 points... remember that the new ranking system the UCI uses to determine who's in the worldtour is based on the previous TWO seasons. That means that even if Frank and Andy both did absolutely nothing the rest of the season, they'd have the points from 2nd and 3rd in the 2011 Tour helping them, as well as Frank's classics placings, etc. And also, the WorldTour ranking (which is what I'm assuming you're looking at) isn't the ranking used to determine who's in the WorldTour.
Basically, getting the Schlecks would assure Riis of ProTeam status for next year. Plain and simple.