I don't recall 220 significant fixes in 10.4.3 or 10.3.3 or even 10.2.3.
Among those improvements are tweaks to the performance of certain graphics drivers and fixes to parental controls, wireless certificates, and screen sharing, those people say. The latest additions bring the running total of fixes expected as part of the release to a staggering 220.
OS X 10.5.0 was a really buggy release. I'm glad I haven't updated yet. With 220 big fixes in 10.5.3 I'm thinking of waiting for 10.5.4!