There is no technological reason for a Chinese database to have limited characters, if it is based on unicode character sets. Its either bad software, lazyness, or another motive.
BJ Klintoon made sure they had the most advanced software available, the Chinese have never struck me as particularly lazy, so my money is on another motive (and I have a pretty good idea of what motivates the Chicoms).
Unicode doesn't even contain all of the old literary Chinese characters yet. If they were being fair and practical, they'd base the limit on the current state of Unicode is (that's considering that they actually use Unicode).