Leg
I think you can be perfectly right but that would depend on the area and even more on the region of the world you are in.
In the USA, city dwellers have weapons and they would represent more of a match. Moreover, from what I know of rural communities there, they are very open and hard to defend. Therefore, I have no doubt that your comparison with locust is quite accurate. However, I guess that things will be very different in mountainous regions and deserts (as described in the game by the way).
I don't know for Australia, however. Also, that won't be an issue as, in my game, Australia remains pretty much in shape and becomes one of the world leading power.
I would expect what you describe to occur also in Russia but in that country the main defenses would be distances. In most of Russia people leaving the cities would never reached the rural villages. Moreover, people coming out of the cities might not have much in term of weapons. The rural areas in western Russia could be more vulnerable but these in eastern Russia would be pretty much unspoiled (however, they are fairly poor).
No clue for Asia, at all.
Things would be very different for Europe, however, IMO. Many of our villages (and small towns) are much easier to defend, they could easily be fortified (when they don't retain some kind of fortification already), and most people coming out of the cities won't have much in term of weapons. Of course, we can also often count on an old fortified or partially fortified castle (14.000 in France Only) from the middle ages. Taking such a castle without heavy weapon is nearly impossible and very few people can stand in front of thousands. Don't forget, that these places usually include several wells.
As a result, I can see several situation that can arise.
First, the most modern village would be wiped out much as what you think.
Second, the vulnerable old village still holding a castle (or a fortified church) will rely on these structures for defense. Life will be harsher there but they could resist. They are politicaly interesting as many could soon be ruled by petty dictators.
Third, the old villages that have been built on a defensive position will be quickly fortified again and they will resist most invasions.
The villages and Towns still having some kind of fortification (and I know hundreds of them in Belgium, France, Portugal and Spain alone) will see them rebuilt. They will not have to fear much outside of military units. Like in the middle ages, marauders will simply avoid them.
I have put a picture of a village located 10 miles away from my place. That village has a population of 700 (when all the population around would have been assembled behind the walls). It is not entirely obvious from the picture but it is only vulnerable from the back. Then, you'll only have to defend a fairly small area (about 30 meters wide) while the other sides would be much easier to defend. Of course, it would need some work to be battle ready but not that much. You'll need to clear the forest and to destroy a few houses in order to increase the efficiency of your defensive walls (then, you'll have to raise them again asap). Antoher, thing, in my region, such village type is not an exception it is the rule. IMO, with the chaos following the first nukes such village could stand even a few thousand people (In Europe and in such village, you'll find at least one firearm in every house while the citydwellers can count on 1 for 100). However, work must be done if they intend to last but I have no doubt that this will be the case almost immediatly.
Of course, I'm not saying that the European countryside would be unspoiled, but several communties would be capable of resisting in a better way. Another thing is that over the past 50 years several of the old time machinery have been restored by historical associations (these would be quickly turned to use again). Most old village can count on a well, on a mill, and on an old oven (not to forget a few generator: 4-5 in my village alone).
Another thing to consider is that after the first incident, country people will shoot almost on sight. Of course, you'll have several thousand refugees but they will be weakened, most will be fighting among themselves and it will take some times before they organize. Yes, a thousand might be threatening you but they will most certainly attack as isolated, disorganized groups. Marauder bands would certainly appear later as a result of villagers organizing their defense.