That DPreview thread is awful.
The only actual comparison he gives us between the sigma and pentax is a crop at 70mm, and he doesn't even bother to mention where in the frame this crop is from. The sigma and the pentax look equally mediocre here. Then he compares it to a FA24-90 at 68mm, which obviously blows both away. Ok so, a lens with a less ambitious zoom range at 75% of its maximum reach is better than other lenses full tele. Moreover, if the crops are from the edges, he's possibly comparing the borders of a FF and APS-C lens.
If you look at the photozone.de tests, you'll see there's not much in it between the 16-45 and 17-70. The 16-45 is sometimes a little sharper in the center, and surprisingly the 17-70 is sometimes a little sharper in the corners, but other than that both lenses are more or less similar performers. The 16-50 has the best center resolution out of the three, but isn't quite as consistent with the border performance.
Seeing that the 17-70 is so close to the 16-45 we all know and love, it does represent a rather attractive option as a standard zoom. I might be tempted to try and replace my 16-45 with it.
However, the x-factor here is color rendition and micro-contrast. Most of us already have 16-45s or 16-50s, or have opted for the sigma 17-70 if we really wanted the reach, so nobody seems to be buying the pentax 17-70. As such, I've seen almost no pictures from the new lens. The 16-50 is well proven in that regard, and day by day my 50-135 is making me less and less happy with my 16-45.