First radiosity, HDRI, Global illumination, etc are all different things and aspects of lighting. Regular Bryce settings doesn't bounce light off of objects. Once a light ray hits an object it stops. This isn't how real light works. All surfaces (except maybe flat black) reflects some light back into a scene picking up some of the color it reflected off. This basically is radiosity. True ambience seems to come close in some situations. Global illumination is a part of radiosity as that light isn't coming from one source. An object is lit by the main light source and the light rays bouncing off of all the objects surrounding it. HDRI is getting the smae effect without having to use any lights especially a light dome which will increase render times. It does this buy reflecting the surrounding image on the object. The only place you really get hard light is from the sun on a bright day. There are some soft shadows outside if the object is tall enough and transmits it's shadow far enough along the ground. Even then you get diffuse light from the surrounding sky. Same thing happens indoors except you get more soft shadows. Basically to light a scene so that light comes from different directions requires you to use multiple lights and manually place them so they match what you want. The techniques descibed above are a way to achieve the same thing with less steps and in a lot of cases less render time and more realistic lighting environment.