The difficulty is that the Lotro Store data is web browser data. The only place the data exists is on the PlaySpan servers. One the reasons that the web store is so slow is that a Turbine's custom web browser is being loaded within the Lotro client software and a secure connection being the web browser and PlaySpan servers. I suspect that to prevent old stale information that is no longer valid from previous queries and sessions. Nothing is cached. That way you always get the current right data. There is always the possibility that a Quarter Master might be updating the Lotro Store while you are using it.
The other issue may be that PlaySpan and Turbine are not using an server side implementation - hardware and software that is fast as a company like Amazon does. Amazon probably spend billions of dollars getting their system to place it is today. Amazon has the problem of a non captive customer base. People get annoyed with Amazon they go somewhere else to get their product. We do not have that choice.
Unless stated otherwise, all content in this post is My Personal Opinion.