I got to thinking about the iPhone 2.0 firmware again and remembered that Applications will have the ability to auto-update themselves. This could be a huge improvement for the device. This may actually allow fewer firmware revisions.
For instance, if you have Mail.app that has a problem you do not have to do a whole firmware upgrade to fix the flaw, you just have to update that application. This could bring quicker updates to applications and make overall security with the device better. The other positive aspect of this is that unless there is a kernel update needed, there may not be as many firmware upgrades coming out of Cupertino.
This however, could also have the reverse effect and actually increase the frequency of firmware updates given the fact that Apple will not have to worry about updating the applications that are typically included with the updates. This could also decrease the size of the firmware updates since the apps will not be included.
Just a thought that I had over the past week.