I was actually just working on this last night. It's a little more complicated than that. Three of the schools with the best placement record (ie. highest percentage of students securing TT jobs) included UCSD and UMass, programs outside of the top 20. NYU has 57% of its students receiving tenure track jobs; UCSD has 78%. The number I used to calculate this stuff came from the APA report on grad schools (although a few schools I had to use their website including UMass). When you plot ranking versus TT placement rate, the plot is pretty scattered. Doing a linear regression, the Rsquared value is about .09, which is a weak correlation between ranking and placement.
I'm hoping to put something up blog-like with some of this information today or tomorrow, if anyone would want to check it out for themselves.