if they allowed search for 3-ltr words, could tie up small server farm with multiple requests.  I've noticed forum pages always load slow on my 125 Mbps conn.

however, just tried google: "the" gets >25 billion results and "koi" gets >82 million, both in <1 sec.

The above could be addressed with caching queries for a a length of time, and other aspects of proper system/database design.