I think Obama is simply aying things in order to avoid thinking about them
Why Mars, or the asteroids, are seen as a more realistic option (when you are too broke to try for the Moon) is a little beyond me, but certainly, the asteroids are a given, if you are thinking about Mars.
Riding on (or, more probably, in) an near-earth asteroid such as 3753 Cruithne is probably the only realistic means by which anyone will get to Mars in the foreseeable future: it is the only type of object that could easily hold the sort of shielding from solar flare activity - like that of last week - which would inevitably have killed the occupants of any sort of normal space vessel. In fact, the likelihood of a lethal radiation event occurring within the time frames required to travel both to and from Mars using a rocket, make any such journey far too hazardous to be worth contemplating. Take the crew, or take the radiation shielding needed to keep them alive: pick one.
Even so, going to one of these asteroids will be a major undertaking, in itself. For instance, at it's closest approach, Cruithne (which, at 5 kilometers long, and locked in a well-synchronized orbit, with the earth, is probably the most likely candidate for a Mars trip) is still more than 12 times as far away, as the Moon - and moving rather faster.
Furthermore, Cruithne will not be making any useful rendezvous, with Mars, for another 48 years, and even then, the trip from the asteroid, to the Mars surface, will be another 9 million miles (assuming someone is aboard, to attempt the journey in 2058). The travelers will then probably have to sit on Mars for some years before another useful approach by the asteroid will occur, in order to allow them to return.
Given all these factors, I cannot see why you would not want to go to the Moon and back, a few times, before attempting it, since this would give considerable practice in using rockets outside of the Earth's protective magnetic shield (thus providing some insight into whether rockets will ever provide a viable means of deep space travel). It could also provide experience in surviving for prolonged periods on an alien world - an almost inevitable prerequisite of any trip to Mars (however you imagine getting there). At this time, no one has even attempted to survive the Moon's lunar night time, on the surface: that's 100 kelvins (-173 degrees C) at the equator.
Too much Star Trek has meant people underestimate how difficult this 'space' stuff really is. Maybe the world's public need reeducating in just how much of an achievement, something represents, before deciding whether it is worth doing? It's either that, or dwindle into extinction, playing Eve Online, and watching David Cameron films about how rotten we'd all be if we actually did get out there.