I will leave it to Don to make the final decision on versions, but I think you were right in most respects. If I am working on the kernel and fix something (not a major new functionallity) then definitly bump the version up. You only need to bump the requires on a package that absolutly has to use the new version. If it is just a code fix or addition of a proc or something the APM should be working to know version >= 4.5.
I thought there was a doc on versions or at least a mention of it somewhere. We should have a standard on versioning though. The original intent at AD was that the core was released with the same major.minor version, but all the non-core packages could have their own versions. This got screwed up and you get packages like news that are version 4.1b. This says it is version 4.1 beta (the letters are supposed to mean something). In reality this package should be named .1b or 1.0b to more accuratly describe it.
I hope this makes sense and it should be on the development do's and don'ts somewhere.