Question about connecting Luxeon LEDs in flashlights?

Pardon the ignorance of a newbie: All the Luxeon LEDs (I, III, and K2) state not to connect the slug to either anode or cathode. I'm under the impression that most flashlights use the body as both the negative contact and as a heatsink (which is attached to the slug). Aren't most Lux's slugs epoxied to an aluminum heatsink which is then screwed into the body of the light using the body to pull heat away from the aluminum heatsink and the Lux? If this is the case, isn't the slug and the cathode electrically connected via the body of the light and not isolated?
Or is my understanding completely off?

Thanks.

There's been some talk of this lately... the general practice when building a Magmod is just to put it on the heatsink using some generally non-conudctive thermal epoxy such as Arctic Alumina. I've probably done 15 of these builds and as far as I know, they're all still going strong.

Now, the red, the red/orange and the amber Luxes have a positive ground so extra caution needs to be exercised with those.

What light are you thinking of modding?

I'm looking to modify a TM-313X, a TM-310H, and possibly one of those rechargable V2 lights that UnknownVT reviewed. This is also a general question so I have a better understanding.
I recall reading often, especially in the custom forum, where people touted their lights to have a heatsink with a lot of thread engagement to the body for max thermal transfer. If that's the case, then the slug of the Lux is connected to the heatsink which is connected to the body which is connected to cathode of the Lux and thus not isolated. Is this the case?...or am I missing something?
Thanks.