The examples may be "artificially" hard, but, aren't they still hard? And, by your own definition (solving big problems=hard problems), don't they still qualify as big problems?
It's true that big problems have to be "hard" in some way, or it would be presumed that these problems would already be fixed. However, in ordinary usage, problems can be made difficult by something that is not technologically or intellectually challenging, but by something that is just practically difficult.
I think a good example would be Dwolla. Or, you might consider deposing a cruel dictator a "big problem." But it's one that was made difficult by the "artificial" challenges of rallying the right type of support, circumventing corrupt government institutions, and so on. Dealing with institutions that have made change difficult is a real and non-trivial concern, even if it's an "artificial" one.
At the same time, the Millennium Prize problems are arguably some of the "hardest problems," but people don't run around talking about how they're the world's "big problems." It isn't implausible to say that solving problems that affect people significantly may be considered "bigger problems" or at least more worth solving those that are not.
On a somewhat related note, I think some of the most important "big problems" are those which are technologically challenging and practically challenging because of current moral fashions. Many of us here may think it important to get humans to a self-sustaining colony off Earth. But most people today don't at all consider it one of the world's "big problems." Still, I think we can do it...