Actually there is a huge difference in delay (ingame only) based on a server that was just rebooted or a server on for 16 days. I dare you to let Xanadu go 16 days without a reboot and people will be complaining hard. I can move to one island which was rebooted a day ago and go to another island on day 16 and see a big difference when you are crafting / imping / using wurm assist to track skill progression.
Obviously there is a issue someplace in the code ( memory leaks ? bad driver? Old version of SQL ? ) but weekly reboot windows give you repeated attempts at resolving the issues. It is difficult to ensure you resolve a problem without a weekly maintenance window.
What is the size of the tempdb on 16 day servers? Is it growing above it's set perimeters? Could be a query over time causing tempdb to get too big.