This news is rather unsurprising, considering that this is Valve's first foray into hardware development and they have been known to take their time on previous projects as well. Their willingness to delay is likely a good thing, as they want to make sure that the product they are making is completely ready for widespread use.
It is a wonder that the Steam Machine and controller are tied together, considering that the controller does not necessarily need the machine to work, but should work on just about anything. However, this news tells us that Valve is not happy with either product as it is at the moment, and the development is a little more difficult than they anticipated.
Then again, it is more likely that Valve is reacting to user feedback, as that is what they point to in their post. They likely had a vision of what they wanted the Steam Machine and Steam Controller to be, but once others got their hand on it and gave feedback, Valve has to adjust. I say all that to hopefully ease the minds of those who are excited for Valve's project and maybe a little disappointed in the delay. The reasons they give for the delay are good ones, so don't fret.
This all comes with their Steam Universe update back in September. With it came the Steam OS, Steam Machine, and Steam Controller.
In the end, those who are at least somewhat familiar with Valve know that they have to wait a decent amount of time to see the end product.
Read more about what companies are going to be making the Steam Machines here.