That can't be correct, because if you take a fresh installation, it should have all the dependencies it needs. But then if you run ipkg upgrade after that, then it will start adding new packages which aren't depended on by your existing packages. I tried running it with the '-force-depends' option and it didnt change anything.
I don't know exactly what ipkg upgrade with no arguments does, but it doesnt just upgrade your installed packages and dependencies. Also, I ran 'ipkg upgrade' after a fresh install of OZ 3.5.4 on my collie and I ran out of space on my root partition.