I think you guys are confusing "Arctic Alumina" with "Arctic Alumina Epoxy." Arctic Alumina is a cheap heatsink paste from the guys that make Arctic Silver. I personally like it better for a few reasons - easier to clean up, cheaper, easy to spread (compared to some). IMO it works "close enough" to Arctic Silver that I personally wouldn't pay the difference. If anyone else wants to pay more for the Silver, that's their own coin.
As for the AA Epoxy stuff, it is just heat transfer epoxy. If you need to attach a heatsink to something and have no other way to mount it, then use this stuff. It is more or less permanent, but can be made kinda-sorta non-permanent by mixing in a bit extra Arctic Alumina (or whatever other compound). That works because it basically weakens/dilutes the epoxy bond. You'd have to experiment with ratios as there isn't anything set in stone (pun intended).