If you had to look up this stat block, it's because your party was being naughty. I'm sorry :(

I think the art for the guard and guard captain got swapped. This stat block has chain shirt, shield, and spear. But the art has a breastplate, sword, spear, and shield. While the art and stats for the guard captain is the opposite. It doesn't really matter but esthetically I love these low level NPC soldier type stat blocks and the associated images. So I'm definitely spending too much time over analyzing them

Here is an additional (Special Action) that I believe adds to their effectivity as a guard.

Raise the Alarm! - If guard is not in a secluded location a guard may use an action to raise the alarm. By using a whistle, ringing a bell, or shouting, the guard can raise an alarm which brings an additional guard every 1d4 rounds, this effect stacks for every guard who raises the alarm. 

** I would also love to see the creation of different 'ranks' of Guards. Perhaps a 1/2 level Corporal. Level 1 Sergeant, Level 2 or 3 Lt. Since there is already a Guard Capt. at level 4. This would help to build command structure. While I know I can build these on my own in homebrew, it simply would be nice to access these in the encounter builder as pre-built NPCs; saving so much prep time. Thanks!

Why was this one updated?  Literally nothing changed except to take away a dual wield attack.  I thought the monsters were supposed to get stronger with the new players handbook buffs to heroes.

I believe they took away the two-handed attack to prevent confusion, since it would need to doff its shield and its AC would be impacted. This is otherwise exactly the same, but if you look you'll see that many other monsters got upgraded substantially. It's not like base line guards were ever going to provide a real challenge to PCs anyways.