Because hidden changes to prepare and allow for the decals will have been included in this patch. For example, I bet the P4 model change is so theres a flat space for decals.
I posted this in another thread, but:
The model change is completely unrelated. Adding decals to the old Panzer IV would have happened automatically because the old Panzer IV already had decal spots (balkenkreuz's and etc). Plus adding Ost camouflages to the new Panzer model and making a stubby gun version is much more work than just altering decal locations.
Seeing as Ostheer's old Panzer IV (as well as multiple other vehicles) was ripped straight from CoH1 with slight updates, Relic probably sought wanted to replace it with the higher quality OKW Panzer IV model. Personally my only problem with that is the OKW version is ever so slightly smaller, and the high quality makes it stand-out among units like the Flakpanzer or Brummbar which are supposed to be built on the same chassis.