Dino had written a post on this.
My view is that the US attitude to, and involvement in, Latin America was dictated in part by the Monroe Doctrine.
The perceived involvement of the USSR in affairs there drove US policy and interference. Sri Lanka is small, distant and has little strategic value unless the Chinese are indeed pursuing a "ring of pearls" policy across the Indian Ocean.
For the US this could be a concern but it is a much greater concern for India, hence the active involvement of India. The
warm relationship that Sri Lanka enjoys with Pakistan in contrast to the colder
one with India doubtless contributes to Indian suspicion of Sri Lanka.
Let us not for a moment forget that there are real concerns over governance, law and order and civil liberties that will cause both Europe and the US to look hard at the country. The Tamil lobby plays its part but remember that there is a never ending stream of people, from the Fonseka family, to the Bharatha Lakshman family to many, many unknown others who, through various channels appeal to the US and Europe in the hope that something can happen, since the systems of justice and law-enforcement no longer work, and indeed are preying on the citizenry.
In conclusion, I don't the the US intends to interfere, certainly not in the way they did in their 'near abroad'. Times have changed and misadventures in Iraq and Afghanistan have taught them painful lessons. However, a domestic uprising if frustration builds to a sufficient level is a real possibility, we have seen ominous rumblings before.
The great saving grace that has prevented this so far, in my opinion, has been the flight of the young. They leave in droves, to the Middle East, to Japan, to South Korea, to Italy, indeed anywhere where they can get a toehold. The Arab Spring was driven by the unemployed, youth as long as we export our frustrated people the country will not reach a boiling point. The added advantage is that the monies sent back, help keep the local economy alive. Virtually every family has some one abroad who sends money back that helps pay the bills and keeps everyone, including the Government happy. Not only will they have no trouble, they can even boast that economy is doing well, even as private consumption is sustained by foreign inflows.