No, the post-M10 contact probably does not mean that Peddie and Mercersburg are more interested in your child than Thacher is. I believe that many, if not all, accepted students are getting similar contact from the first two schools. We were in the same boat in 2012, with a barrage from Peddie compared to just a call from other current parents at St. Andrew’s.
The differences might mean that M. and P. consider themselves in a more competitive admissions environment, while T. and SAS are more comfortable with their historic yields. I wouldn’t be surprised if they vary, in percentages, from the 30-40s on the one hand to the 60-70s on the other. Focus on approaching the revisits with an open mind, even if you have already “ranked” the schools. What you learn about the schools before the revisits may be important to you, but don’t give much, if any, weight to the mere fact of this reported communication.