They probably included the beta software update application so they could test its use in the beta operating system.
There will probably be updates every now and then before the release (no evidence just based on gut feelings). But keep in mind that this is a beta release and Apple has warned you about using it as a production machine.
Apple is under much less pressure to get bug fixes and updates out the door. Might users loose all of their data accidentally? It's a beta. They were warned about this. Might users be desperate to use Airport or other hardware? It's widely public. We need to make sure we get them very close to finished or we'll have very bad PR for writing sloppy code. Or take the case of the Java developers, on the MRJ mailing list they say that they are in a bit of a quandry as to how to update their software on Mac OS X since it's integrated at such a low level. Even if there is stuff in the pipeline to be sent, Apple may not have figured out HOW to update it.
If Apple is getting quality feedback from users of the public beta then they would be reckless not to use the opportunity to test updates. But I'm sure they are under much less pressure to get updates out for a beta OS.
Apple is rumoured to be working on an update to the Public Beta, as well as Microsoft working on an update to MSIE 5.5 ( The version included with the Beta ).
Fixes reportedly include a patch to OS X's network code to prevent a possible denial-of-service attack, updated storage drivers to prevent installation problems on certain new Macs, and numerous small changes to the BSD UNIX layer to deal with known multiplatform issues in certain command-line utilities. Some reports suggest that a patch to Microsoft's Internet Explorer for OS X will also be included, but this has not been confirmed.
I also have a good connection with two people working at Apple that have low level clearance. I find out some info mainly about software development, and other minor things, like new iMac and iBook colors. They were able to confirm that an update is being worked on in light of the fact that so many more people bought the beta than ever anticipated.
The timeframe for it's release, however, remains unknown