It should be mentioned that even with weedblock material, you still have to weed those gravel areas. The difference is the weedblock makes it much easier to pull up the weeds. They will grow in the dust and sediment that settles on top of the weedblock. You can spray large gravel areas at weed killer, but it can leech into nearby vegetation. If you drive over gravel with weedblock under it, it will shred the weedblock eventually.
I've used a liquid pre emergent the last few years on my no grass landscaping in StG, left the house for 2 months and had 10 minutes worth of weeding to do when we got home. Before using pre emergent I would weed for 10-15 minutes/week. I should add that my front yard has no weed block, rocks over dirt.