Canalys researcher Tim Coulling is saying that it's all about the price, which for both the RT and Pro versions of the Surface "will be too high to capture significant market share". The official recommendation from the firm is that OEMs hold off on making any Windows 8 tablets until "Microsoft rethinks the high license fee". Then he dropped the Z-bomb in saying, "We expect the Surface pads to have a similar impact on the PC industry as Zune did in portable music players." Ouch.
Of course, the analogy, as harsh as it sounds, may be pretty accurate. The Zune wasn't really a bad media player and Coulling doesn't seem to see the Surface as a bad tablet. It's more a matter of launching in a very tough market at a price that isn't competitive enough. Like it or not, the iPad is still dominating the 10" tablet market (although Samsung and Asus are growing fast), and has proven itself as the only $500 tablet that people are willing to buy. The only reason the Kindle Fire or Nexus 7 have been successful is because of the price point, which Microsoft just can't match.
It does really seem like Microsoft is aiming for the enterprise market with the Surface though, so success will be measured on quite a different scale than for consumer products like the Nexus 7, Kindle Fire, or iPad. As always, time will tell.