Joe Carter points out something that seems obvious to us professional science types: scientists have a tendency to hype their own areas of research, glossing over difficulties. There are various reasons for this.
First, as Joe mentions, there's the money angle. For some fields, the potential for entrepreneurial success teaches scientists salesmanship. For most scientists, however, it's a matter of writing grant proposals in order to convince government and industry funders that you can do the research that they want. That money doesn't usually go directly into your paycheck, but it does allow you to hire more graduate students and postdoctoral fellows, to buy more equipment, and overall to do better research. That, in turn, brings you the more important coin of academic research: prestige. The better the funding, the easier it is to do better research, publishing more papers. Now, when discussing your research among your peers, overhyping your work can have a detrimental effect on prestige, so you need to be a little less enthusiastic in your peer-reviewed papers, but not too unenthusiastic. When you're talking to sponsors, however, you're a salesman, and that means putting a positive spin on things.
Second, when all you have is a hammer, all you see is nails. Most scientists went into their respective fields because they saw potential in it. They don't give up their initial optimism easily. So they are always looking at problems and wondering whether their particular field can help. It may be true that some other field is more likely to solve the problem first, but no scientist understands--or trusts--other fields as well as he does his own. His natural inclination is to think that his research holds the most potential to help, and it takes a bit to convince him otherwise. My particular specialty is superconductivity, and for a long time now, it's been a solution in search of a problem. I'm just hoping that quantum computation is finally it.