The tricky thing with ESD is that even when it doesn't seem to affect anything, every small discharge does cause some damage, whether it's pitting of the silicon, vaporizing a little bit of the bonding wire, removing some of the metalization on one of the semiconductor layers, or some other effect, it will physically alter the product.
In most cases, most uses of a given part won't be measurably altered by the change. Most people overengineer their designs so they aren't using them anywhere near their limit, so there's a huge margin where a pitted part will work just fine for more uses.
Over time repeated discharges will change the part enough that it will behave slightly out of spec - but perhaps not enough to notice without thorough testing. This is really the worst case scenario - since it works most of the time, then it's really difficult to find out why it's not working when it fails. It's far better for a part to fail completely so it's easy to track down.
Alternately, the one small discharge that happened once damages it enough that when you do use it to full capacity, it then fails. The happens, of course, once you've deployed it in the field and it's a pain to get it back and troubleshoot it.
This kind of damage cannot be detected without removing the silicon from the package and inspecting it, or, in cases where the damage is hidden inbetween layers, by slicing the silicon into very thin sheets where the damage is likely to occur.
So yes, everyone here is right when they say, "I rarely follow ESD precautions and I have never seen an issue." They will never see it, and when it does fail there will be no reason to believe it was ESD related because there was no recent ESD event.
But that doesn't mean I'm going to trust the products that come from their bench, either.