Ironically, in all likely hood, both of your questions are true statements.
The socket that both these CPUs reside in is called LGA775. It's being phased out..
The E5400 is an earlier release, (and lower tier), than the E6500, which is the latest and last Pentium Dual Core LGA775 CPU that will be produced.
So, the all E5400s were probably gone, and you lucked into the better processor.
The E6500 is the most potent of this series of Intel CPUs