I think the biggest problem is that lots of users don't even bother to read the full thread before posting (or even quickly view it).
Having the post button under every post would even make it worse IMHO, relocating it a little higher could be better (immediately under the thread for example) but that could become a whole different discussion with many different opinions.
Not being able to easily quote only parts of the first post fully formatted (bbcodes included or most of them) is very user unfriendly too (at least I think so), unless you could still do it from posting history.
IcyPhoenix already misses the feature to be able to highlight part of a post in posting history and quote only that part with a push on the quote button (something I've been told is very hard to achieve after suggesting such a feature)
In short ..
The code suggested by TopoMotoV3X at our Italian site has upsides and downsides but personally I would not expand on it making it block even more... but that's just my opinion