The reason people are doubting the spoke flexing description, is that there's nothing holding on to the rim end of the spoke. If you put enough force on the rim to cause it to deflect (bend towards the hub), the spokes on that side wouldn't bend, they'd just push deeper into the rim. The only way to see spokes flex is if you put a large sideways load on the rim. And even then the amount of flex you're likely to get is too small for a rider to easily see (though it can often be felt).

The amount of curb hopping, pothole smashing madness your bike can withstand depends on the rider and how you ride. A 140 lb rider going off a curb is going to have a lot less energy to absorb on impact than a 240 lb rider. But how quickly the energy has to be absorbed also makes a difference. Using your legs to dampen impacts spreads out the energy with respect to time resulting in much less stress on the bike (and the rider). If you're going off curbs with your butt planted on the saddle, neither you nor the bike are likely to tolerate that abuse for long

The fact that you haven't mentioned flats says that you're probably not riding as hard as it sounds. The tires on the bike are taking the brunt of the impact energy. If you push too hard, you'll start to suffer pinch-flats where the inner tube gets pinched between the tire and the rim on hard impacts and gets a little hole on each side. Assuming you're not getting those (and that you haven't pumped up your 35c tires to 120psi to avoid them), you probably don't have much to worry about.