Typically, the distributors are just as conservative as the manufacturers, and just as cautious about dealing with newcomers and new ideas. Even if they agree to add a product to their catalog, the distributors can easily decide not to encourage their representatives to promote it, which means that in a few months they have effectively removed it from the shelves.
Of course, online sales are a possibility. But meanwhile, the hardware has to be stored somewhere, adding to the cost. Production runs on demand are expensive even in the unlikely event that they are available, and even unassembled units need storage.
I have been generalizing wildly here, but anyone who has ever been involved in producing anything will recognize what I am describing as the norm. And just to make matters worse, open hardware producers typically discover the situation as they are going through it. Inevitably, they make mistakes, which adds still more delays.
But the point is, if you have any sense of the process at all, your knowledge is going to change how you react to news of another attempt at hardware. The process means that, unless a company has been in serious stealth mode, an announcement that a product will be out in six months will rapidly prove to be an outdate guestimate. 12-18 months is more likely, and the obstacles I describe may mean that the product will never actually be released.
For example, as I write, people are waiting for the emergence of the first Steam Machines, the Linux-based gaming consoles. They are convinced that the Steam Machines will utterly transform both Linux and gaming.
As a market category, Steam Machines may do better than other new products, because those who are developing them at least have experience developing software products. However, none of the dozen or so Steam Machines in development have produced more than a prototype after almost a year, and none are likely to be available for buying until halfway through 2015. Given the realities of hardware manufacturing, we will be lucky if half of them see daylight. In fact, a release of 2-4 might be more realistic.
I make that prediction with next to no knowledge of any of the individual efforts. But, having some sense of how hardware manufacturing works, I suspect that it is likely to be closer to what happens next year than all the predictions of a new Golden Age for Linux and gaming. I would be entirely happy being wrong, but the fact remains: what is surprising is not that so many Linux-associated hardware products fail, but that any succeed even briefly.