Although Apple will continue some limited support for older versions of OS X in the form of security updates, there will be no further incremental updates for older major versions after a new major version has been released. When 10.5 is released there will be no further updates past 10.4.x, but there may be security updates for 10.4.x for some period of time. Since the release of Tiger Apple has provided two or three security updates for Panther but none for any earlier version. It's reasonable to presume a similar pattern into the future.
However, only Apple knows. No one here is an authorized representative of Apple so anything we assume here is purely speculative. Speculation is considered an inappropriate use of the Discussions according to Apple's Terms of Use.