In Iray, like every other PBR render engine, you get realistic shadows. They are, generally, not going to be as sharp as you are used to with Firefly, 3Delight, Lightwave, Carrara etc. but they are there.

Note what you are talking about is the same things that photographers have been talking about for years. :)

Two things will influence your light in Iray. First is the light itself. You have the intensity of the light, and the distance of the light from the target you want lit. The second thing is the Camera settings (which are actually on the render settings under tone mapping).

You can't take a camera and set it for a bright sunny day (the default tone mapping setting) and take it inside turn on a single 1400 lumen light (About 100 watts) and expect the image to be bright or well lit.

Just like with a camera sharp shadows can be done in Iray, or other PBR render engine, and you basically have to set up your shot the same way. Here are a pair of examples. One lit by a daylight HDRI

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This one is an interior shot using a Paramount Light rig, that I built based on information in a photography book.