The tipitaka.org search engine seems to be different from the one they
use on the CDROM. For one, the online web based search was developed
later (just "recently"). Then again, i noted a difference between the
one hosted on the tipitaka.org site and the one you can get for free
from the company which created the tipitaka.org search.
The most "reliable" results so far i would get from either Frank's
CST4's desktop based search (backed by Lucene, for the programmers
among you) and with tipitaka.org's "Accelon 3" listing all occurances
of a word.
I think those two might even provide better results than the old CSCD
CDROM because of some spelling corrections / bugfixes in the meantime.