It is true that Cisco tell you not to use subnet zero and yet they have it enabled. It actually gets worse as i teach CCNA 1-4 whist studying CCNP!!! In CCNP you can use subnet zero. There are times when my brain wants to drip out of my head!!!!!
I can confirm that Cisco assumes Subnet 0 is not usable on the latest CNNA course as I was teaching it a few months ago. I really do not see this changing in the near future either.
The fact the CCNP does make use of Subnet 0 also makes some sence. A CCNA candidate cannot be compared with a CCNP candidate in terms of knowledge and experience, and I believe that Cisco also see's it in a similar way, by 'allowing' the use of Subnet 0 in the CNNP course.
Topics like subnetting and IP Addressing run in the vains of a CCNP, where as a CCNA usually hears these networking terms and turn the other way :!: