When installing fixtures in clothes closets I have always considered the horizontal distance from the face of the fixture to the shelf when determining the clearance from the "nearest point" of storage space. Since the intent is to keep hot fixture parts from contacting or falling on storage items it seems that clothes hanging from a pole would infringe on the intent of the code but they most likely, measured diagonally would meet the clearance requirements. Are the parts supposed to be cool enough by the time they reach the clothes? What exactly is the definition of storage space since a clothes closet could be jam-packed?
From 2014 NEC... 410.2 Definition. Closet Storage Space. The volume bounded by the sides and back closet walls and planes extending from the closet floor vertically to a height of 1.8 m (6 ft) or to the highest clothes-hanging rod and parallel to the walls at a horizontal distance of 600 mm (24 in.) from the sides and back of the closet walls, respectively, and continuing vertically to the closet ceiling parallel to the walls at a horizontal distance of 300 mm (12 in.) or the width of the shelf, whichever is greater; for a closet that permits access to both sides of a hanging rod, this space includes the volume below the highest rod extending 300 mm (12 in.) on either side of the rod on a plane horizontal to the floor extending the entire length of the rod. See Figure 410.2. 410.
My opinion is that the fixture is to be far enough away from any combustible materials that could be ignited by the heat generated from the fixture. The 'hot' parts that you refer to are supposed to be contained by the fixture, as bare bulbs are not allowed.
And yes, I have seen some really 'packed' closets, and some really scary means of illumination.
Observed abuses aside .... and anything can be abused .... the code does provide for specialty luminaires to be installed closer to stored materials than you might expect from the excerpt posted above.
For example, there exist illuminated closet rods that, by their design, can't help but place the cloths much closer to the light than 12".
I expect hat with the expanding use of CFL and LED light sources, as well as the legislative assault on the old-fashioned incandescent light bulb, that closet lighting will soon stop being such a 'hot' topic.
Now, does putting an enclosed bulb, or a CFL bulb, into an ordinary fixture make that fixture either enclosed, or fluorescent, under the NEC? Good question.
Early on, the IAEI took the position that no, it does not. In a like manner, California took the position that such did not make the fixture energy efficient either. Both justified their positions in that you "might" later put an incandescent bulb in the fixture.
I do not see anything in the NEC, or the various energy codes, that allows for such an interpretation. Not only is such an approach an affront to our concepts of right and wrong (do we ban cars because they MIGHT be used to commit crimes?), but Article 90 of the NEC makes it pretty clear that what 'might' happen in the future is beyond the scope of the code.
I had one of the LED proposals that were rolled up into that code change (accepted in principle) 410.16(C)(5)
410.16 Luminaires in Clothes Closets. (A) Luminaire Types Permitted. Listed luminaires of the following types shall be permitted to be installed in a closet: (1) A surface-mounted or recessed incandescent luminaire with a completely enclosed lamp (2) A surface-mounted or recessed fluorescent luminaire (3) Surface-mounted fluorescent or LED luminaires identified as suitable for installation within the storage area (B) Luminaire Types Not Permitted. Incandescent luminaires with open or partially enclosed lamps and pendant luminaires or lampholders shall not be permitted. (C) Location. The minimum clearance between luminaires installed in clothes closets and the nearest point of a storage space shall be as follows: (1) 300 mm (12 in.) for surface-mounted incandescent or LED luminaires with a completely enclosed light source installed on the wall above the door or on the ceiling (2) 150 mm (6 in.) for surface-mounted fluorescent luminaires installed on the wall above the door or on the ceiling (3) 150 mm (6 in.) for recessed incandescent or LED luminaires with a completely enclosed light source installed in the wall or the ceiling (4) 150 mm (6 in.) for recessed fluorescent luminaires installed in the wall or the ceiling (5) Surface-mounted fluorescent or LED luminaires shall be permitted to be installed within the storage space where identified for this use.
I think this will start showing up more as the LED luminaires get more popular. If you are paying for the listing anyway, adding the endorsement for storage space is just a small incremental cost in the grand scheme of things. As the NRTLs get comfortable with the idea this should be a fairly simple test beyond what they do for any product and that is pretty extensive. They blow things up in every conceivable way to see how they fail but even with that, I am amazed at some things that pass.
I'm amazed at what passes also. For instance, some of the weatherproof boxes and LB's I've used lately seem like they were designed to strip the insulation off the wire when it's installed. Ground screws strip out. Total junk.