Finn,
They don't give us the deltas, we have to determine that on the fly, as it could be a new app install, update, forced repair, etc. Good feedback here!
Actually, it says 400+mb download, but you probably noticed it went pretty fast. In the update process, it will skip many files in the databases. Although the initial download size may say 450+mb, what your data carrier actually sees and charges you with will be less, due to skipping these files. I confirmed this with Brian. You can test it by touching Force Database Refresh and it will finish very fast. We have it on our discussion to look into the to more accurately depict the "net" download size.
There is some basic logic there but it's to keep the update process simplified. I don't think this applies to the charts as there are downloaded as a hole chart, not just portions. It will only update the new charts in a selected state, not all over again.