It kinda depends on how you look at it.
I'd always played it using power chords until just recently.
The reason I wrote the tab the way it is, is cause I saw an airing of "Behind the Music" where it specifically mentions Smoke on the Water and how the chords were played on the album.

The first tab in this thread is also correct except that it's been changed from the key of G down to E and it's played on just one string to make it easier for beginners.