From my understanding, with this rule you don't need to fuse the feeders of a sub panel less than 10 ft. There is usually no extra lugs to tap off a main panel, so you have to fuse them with a breaker anyway. Am I thinking right?
(Just thought about the 25ft tap rule, have to look it up).

There are so many variables in this question that it's hard to respond.
{240.21(B)(1)}If you have a conductor to a subpanel less than 10'long, that conductor does not have to be protected at its ampacity. It can be 1/10 of the ampacity of the OCPD that feeds it.
{408.16}The subpanel, however cannot be protected by a larger OCPD than its rating, so it would have to be protected by a main breaker or a OCPD in the main panel if the sub's rated at less than the main panel's OCPD.

aldav53, they do make panels that have a main breaker at the top for the feeds and have lugs at the botom of the panel to feed a sub panel which is a main lug panel sitting next to the main panel, so in a way the tap is just a continuation of the buss bars