It appears Google
may have slightly altered the hardware design of the Nexus 5 smartphone
to make it a bit more sturdier and better overall. Differences in design were discovered when an XDA Forum member sent his Nexus 5 in for replacement due to several defects in his existing one, including "noisy buttons," a protruding SIM tray, and a few other niggling issues.
The Nexus 5 he received back was slightly different from his defective device. None of the defects he complained about were present, plus it had buttons that weren't as noisy and a larger microphone with bigger speaker holes.
The differences are subtle, though if you peek at the picture above, you can make out ever-so-slightly bigger speaker holes. It's kind of a bummer for early adopters to be stuck with an older revision, but on the bright side, there doesn't appear to be any major advantages. This is purely speculation, but perhaps the revised model pumps out slightly louder sound, or maybe the speaker holes are just less prone to getting clogged up by dirt and debris.
All that said, if you've been eyeballing the Nexus 5, you may want to wait just a little longer before making the jump to ensure that you get the newest revision.