There have been skis that displayed both all mountain and powder characteristics since ski companies started selling specialized performance skis. The definition of all-mountain skis and powder skis has just changed over time as ski manufacturing got more advanced.
All skis outside park/pipe and racing are fatter. As others say, the definition is changing (and blurring). Jeffry is all mtn. Pow is >110mm underfoot, though I personally consider my 113mm underfoot all mtn...