First off, don't be afraid of harder lighting. If you want detailed texture, that's where you start. That doesn't necessarily mean using a speedlight naked (although it can), but the easy-way-out umbrellas and softboxes are not the way to go about creating images like these. When you start with the right lighting, you don't need to do a whole lot in post in order to get this depth of detail.
If I had to guess, I'd say the lighting was primarily from Fresnel spots, although a medium-sized gridded reflector (something smaller than a "beauty dish" but bigger than a standard reflector) or even a smallish gridded softbox would provide the same sort of shadows and texture. Any of these will provide very directional light without the razor-edged shadows of a point light source or a lens spot. That's the key to getting the texture detail in the skin, hair, beard and fabrics.
It helps, of course, that the equipment used was probably not a $50 point-and-shoot and a couple of flashlights. Some time was spent setting up the lighting (probably with stand-ins for most of the work), and the camera was quite capable of capturing the detail. But it's the lighting that's the key.
There is no doubt the picture went through a lot of time in Photoshop, but I would say that very little of that time was spent doing what you think was done. The eyes were gone over pretty thoroughly, there was probably significant retouching around Downey's scar makeup, and there were no doubt skin blemishes and imperfections in the fabric drapery to worry about. The detail and texture, though, aren't the result of heroic post-processing special effects -- they start with good lighting.
By the bye, if anybody wants to combine the strobist DIY way of life with this sort of hard-light, high-detail photography, a Fresnel spot for your speedlights is fairly easy to make. If you can't find surplus overhead-projector resin Fresnel condenser lenses at your local Emporium of Interesting Things (every decent-sized town has one of these, and its presence or absence is probably a good definition of "decent-sized"), then the old mail-order (now online) stand-bys like Edmund Optics can sell you a lightweight resin Fresnel lens. The rest is just fabbing a tube-in-a-tube (or box-in-a-box) to allow for variable spread of the light with the Fresnel lens on one end and a cut-out for your flash on the other. The exact design would depend on the focal length of the Fresnel lens, and how tricksy you want to get with the focusing mechanism, but it can be pretty rough and basic and still give impressive results.