It is a software and server limitation that prevents the server from getting overloaded. The forum software and server database will ignore 3 letter or less search terms. There is a server update that can be done to allow the usage of three letter search terms, but whether or not it will (or rather, should) be implemented is up to the site staff.
HID's counts as three (due to the apostrophe), but hids counts as four and yields results.
Source: I co-admin a V-Bulletin forum and have had this same request from my users.
Thanks for the clarification. I saw a couple of people being chastised for not searching before asking HID questions. I hope they'll read this and be suitably shamed for telling other users to do the impossible.