Water/dirt through the holes
Liquid water can't enter through the holes, the surface tension is far too high, but of course moisture in the air would be able to. Not sure about dirt. Nothing we human scale people think of as dirt would fit, but dirt particles too small to see would. I just don't get why you seem to think this is an issue.
Don't you think the volume buttons on a current iPhone offer a MUCH easier path for moisture and dirt to get inside? Nevermind how easy it is for dirt to get inside any phone where the back comes off to replace the battery, it isn't as though that hermetically seals when you snap the back on. Or all the other openings phones have for charging, headphones, SIM cards, SD cards and so on. Yeah, let's all worry about the micron sized holes!