<p>Its just like geology (my field) doesn't get any respect. My personal opinion is that people are conditioned when they are kids that fields like geology and astronomy are 'lower' sciences due to these screw off classes of which the lower track kids are tracked into. In actuality, they are both very difficult inter-disciplinary fields where you have to draw on all of the traditional sciences to solve abstract problems. </p>
<p>Another secondary issue adding to the problem is that most don't know what you can truely do with these degrees. Most people who go into these fields either had an interest in the fields as a kid (I have a suspicion this is more true for astronomy) or come to the field by some weird set of circumstances (normally the case for geology).</p>
<p>Now, I'm not as well versed in the applicability to astronomy in the employment sector as I am with geology (naturally), but you did hit on two big employers (NASA and USGS). A large number of those PhDs likely stay in academia as either a professor or a research assistant and a number probably go with large aerospace companies such as BAE, Boeing, etc as researchers.</p>
<p>The reason there are relatively few departments in these disciplines (at both Universities and LACs) is because there is a lack of interest in majoring in these fields and likely a lack of funding (typically depends upon which party is in control in the White House...ahem!).</p>