This is correct. And the Founders limited the franchise to accomplish this. I doubt they would look fondly on "Motor Voter" or all the other schemes currently being employed to dilute the vote of those who actually pay attention.
I have a very simple proposal to help stem the decline. Let's make it so that you have to register in person with a valid photo-id 6 months prior to every election. No "provisional ballots" no "same day registration" not even automatic re-registration. If you want to vote in the upcoming election you have to be interested enough in what is happening to get off your duff twice, once to register and once to vote.
This simple reform might also help McStupid realize his dream of getting money out of politics. If the disinterested could not vote, there would be no reason to spend hundreds of millions of dollars trying to win them with over foolish 30 seconds TV ads like we see now during the pre-election circus.
But don't expect this reform to be implemented by the political class. The last thing the politicians want is to have to answer to a voting public that pays attention all the time rather than just a few weeks prior to election day. Both national parties love having the outcomes of elections determined by a vast pool of sheeple who are easily swayed by vague promises of favors that never need be delivered.
Think of this proposal as ACORN in reverse.
FDR