In Dynamics AX 2009 RTM/SP1, the Development team deploys hotfixes/KBs along with other dependent hotfixes/KBs. That is to ensure that they deploy the most updated inter-dependent objects. Thus, that may lead to a larger than usual hotfix/KB file. When that happens the impacted AX objects are isolated (not dependent on other newly updated objects), and the hotfix/KB file is much smaller.
A hotfix/KB is not as big as a release Roll-up (which would already include all the hotfixes released to date for the version).
The MBS Development team also tests the fixes to an issue, as part of the whole KB package, and not individually. If Partners/Customers decide to extract and import objects from the KB package, then Microsoft will not be able to provide them any support on those environments should any issues arise later.
