In the post linked I'd say the correct phrasing should be "manufacturing improvements" as opposed to "hardware improvements." Things such as how the power adapter is made, perhaps the way some things are attached or arranged internally, and possibly a new batch of hardware components (but not different hardware components).
This is pretty standard on new release devices. A good example is the MacBook Air saga. When they were first released the first batch had some serious overheating issues. Apple tweaked some stuff and they problem went away. It wasn't a change in hardware, but more like a possible minor change in manufacturing procedures and a tweak to software.
As for the original question, I got my current iPhone about 1 month ago (it was a new purchase, not a refurb exchange) and it has had a couple minor issues. I do not know, however, if they are hardware or software related just yet (they are just that minor).