As a practical matter this means that one could not sue in the US to enforce an Intrade contract and would have to rely on non-US forums to sue

A commodities exchange in the US tried to offer these types of contracts and were blocked. Intrade is based offshore and would not be legal if based in the US. There are public policy reasons against betting on political races which is why the US exchanges are not allowed to offer these contracts.

with 'no-action' letters.

Iowa electronic markets: http://tippie.uiowa.edu/iem/markets/

CFTC correspondence on: http://www.cftc.gov/foia/repfoia/foirf05-003_1.htm

of course you can gamble on outcomes of real-world events (such as scotus decisions or presidential elections) just as you can gamble on artificial contests (such as horse races or roulette).

however, real-world events have real-world consequences and real-world risks that necessarily must be managed. horse racing for money need not exist, it's an artificial contest. but presidential elections and scotus decisions and the prices of oil and corn and whatnot necessarily exist in our economy, and those risks must be managed. markets such as futures markets serve to let people hedge or reduce those risks and transfer them to other who have more of a desire to take on such risks.

in the case of intrade in particular, it is, or at least it began, as an academic research project. real money is used because a basic premise of the research is that real money is needed to make it work properly, but the idea is not to get rich on it. there is (or at least was, early on) a strict and low limit on how much you could risk, unlike futures markets. in any event, presumably it has merit to the researchers beyond any merit/demerit the market itself has.