The beauty of a free capitalist economy is that competition naturally takes care of most pricing issues.
This is why they try to hide things from us. And sometimes they do pretty darn good job of doing it too.
In the case of the seats one distributor is very reasonably priced, the other main distributor is just as high as Sears but they were before the Sears price hike.
As other parts it takes someone like me to find, cross reference, and keep track of the alternate parts.
Here is an example of the stock record here for the Kohler PN. By checking the crosses I can usually find a better priced part that both saves me and the customer money.
In the case of spark plugs it help reduce the overall inventory of different plugs that are the same just different part numbers.