Abstaining to vote is one of the few ways a populace in a democratic government can show their disagreement and displeasure with the system. Many people abstain to vote, or vote for a particular candidate that has no chance in winning for other reasons that being lazy, or wanting to reward the Republicans. I see nothing wrong with the decisions that these people make, it really isn't much different than voting for the lesser of two evils which you are proposing.
The system is broken, these people see that the system is broken and decide it is not worth it to participate - even if they DID participate, the system would remain broken, because the part that the populace is allowed to participate in has no control over the shape of the system. Understand? Abstaining is how you say the system is broken and that you will not play part in the broken system.
However, instead of the government, the elected officials seeing low turnouts for votes as a sign that people are displeased with the system, they as corrupt individuals in a corrupt machine see it too their advantage - they shock the gullible into voting people in that have no desire to fix anything, and just to make it worse, or they stupidly raise a billion dollars to sell themselves to the people that haven't quite lost all hope in the system - but that will just jade these hope-filled people even more. If we see even fewer people come in and vote this coming election, do you know who's fault it is? It will be the Democrats/Obama, for making false promises.
Tell me how voting for Obama this coming election will start to fix the system and I will vote for him, I'll be the fucking first person in line in my district. But if you are expecting me to vote for the lesser of two evils to maintain the status quo, you'd be mistaken - I'd rather vote for someone that has no chance of winning but more closely expresses my political opinions, than continue to play this broken game.