Hi plasma800,
There are so many different types and designs of innerspring mattresses it would depend entirely on the specifics of the mattress and the type of coils and on how many coil layers were in the mattress (many mattresses that have thousands of coils have two or three coil layers). I certainly wouldn’t assume that a mattress with thousands of coils is better than one that only has a few hundred.
There is more about the different types of innersprings in this article and in post #10 here.
If you are looking at the same type of innerspring where all the other specs are the same then depending on the specific materials above the coils a higher coil count would generally mean more steel and result in both a firmer support system (each coil has less weight to support) and/or a greater ability to adapt to the shape of the body (there are more points of compression).
If a mattress uses coils in the comfort layers (microcoils) that is replacing other foam materials or has multiple layers of coils on top of each other in the support layers then adding these together can result in some misleading numbers.
In the end the difference between them that means the most is what you feel on each mattress in terms of PPP.
Phoenix