Do tourists from other countries need to get an international driver's permit to drive in USA or is the license from their country sufficient ?

No, the US does not require foreign drivers to carry an IDP, which is essentially a translation of their official license.

Here's a link to the FAQ offered by the Registry of Motor Vehicles here in Massachusetts -- your question is #4.

http://www.mass.gov/rmv/license/international.htm

The answer to that question, though, in addition to saying it is not required does indicate that it's advisable to have on if the original license is not in English. It can help at the rental counter, but would be especially important if you are stopped by the police or have any official trouble of any kind.

Well - that answer is correct for Massachusetts. But since each state has different driving laws - and I'm certainly not about to check all 50 - the OP needs to check the laws in each of the states in which they plan to drive - as well as the rules of the company from which they are renting the car.

If it were me - I think it would just be easier to get the license.

It's not a license, it's a permit.

States do not sign international treaties -- they do not individually have the right to require the IDP; it's the US that has decided not to require it, this is not the sort of thing a state can decide on its own to require.