the JDK's JRE has server version of virtual machine called HotSpot(VM which has JIT compiler) addition to client VM. the outer JRE contains only client version of VM.
coming to your question: I think it makes sense to put jre into developer kit, so that everything will be under one place. also you can switch between server and client version of JRE at runtime to produce better code.
I will suppress my every urge. But not this shameless plug: