But perhaps what you should have said is: "Yes, it would validate that block fully -- with his (old) validity rules, in which those opcodes are NOPs, hence it would accept the block as valid." Is that so?
Yes, that is so.
By the way, are those NOPs really NOPs, or do they mean "terminate the verification with success"?
They are actually NOPs. They mean "do nothing" not "terminate with success".
In the original design, the propagation was supposed to occur among the miners, who have incentives to keep the network running and to keep clients happy. The original design depended on those incentives to argue that even simple clients would have adequate security.
The non-mining relay nodes were added later, without any justification. They break that security argument.
Nope, not true. The original Bitcoin Client (v0.1.0) did not having mining enabled by default. When you downloaded 0.1.0 it defaulted to being a non-mining relay node with the option in the GUI to enabled mining if you so desired. In fact Satoshi even said so himself in the original 0.1.0 announcement email:
http://www.metzdowd.com/pipermail/cryptography/2009-January/014994.html.
You can examine the source code of 0.1.5 (the earliest available on github) at
https://github.com/bitcoin/bitcoin/tree/v0.1.5 and you can get the original 0.1.0 client with the source code from
http://satoshi.nakamotoinstitute.org/code/.