Remember that this is a rule of thumb, so it gives you only a general idea. I found I can push this limit to slower shutter speeds, in particular with the help of image stabilisation. But this is very individual: I have training in archery and I can hold the camera very still for a few seconds and I've learned to press the shutter button very gently, without shaking the camera.
This picture was taken handheld at 29 mm using 1/4 s shutter speed, while the rule of thumb would tell me not to go below 1/30 s. If I remember correctly, I crouched and locked my elbow against my legs for extra stability.
Image stabilisation can increase available shutter speeds perhaps by factor four, but again, a lot depends on the photographer.