The same apply with Nvidia. Why did they present something that was not presentable.
They presented Fermi at a tech conference planned months in advance. If they didn't present anything, that would've been cause for concern, so they were basically compelled to show what they were willing to in advance of launch. They also didn't make any direct comparisons to the competition, probably because they believe Fermi has no competition.
This is very different of course to what AMD is doing in this case, as they're basically shadow boxing with unreleased parts when they already have their hardware in the channel. There should be no need for this kind of underhanded marketing, the fact they are resorting to this kind of tactic just shows they're scared, and from what we've seen about Fermi, that concern is probably justified!