Hi Mike,
It's fairly hard to explain the reason for this because the response you posted IS the way the store window is programmed.
I think the confusion arises because once you view one item, the store window becomes cached by our system for 1.5 hours, so anyone who views your items for the next 1.5 hours will see the same items in the store window.
For example, when I view your item at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=4829900777 , which ends in about 3 hours, the items I see in your store window all end in between 4.5 and 5 hours. Then, if I view another item of yours, I will see the same store window and so will anyone else who views your items within the next 1.5 hours.
When each 1.5 hour interval expires, your store window has the potential to display new items, but if the next person who views one of your listings that ends in the same time frame, the items generate for the store window may be the same or similar.
The 4 hour refresh period I mentioned concerns the removal of closed listings and the addition of new listings in their place, but we've actually changed that period to 2 hours.
I hope this makes sense=)
-Mike