If you have a valid visa stamped in your passport to enter US and valid return to the US, you definitely fall under "a valid visa for entry to Australia, Canada, New Zealand or the United States of America and a valid airline ticket for travel via the United Kingdom as part of a journey from another country or territory to the country in respect of which the visa is held; " This will exempt you from the transit visa requirement. Make sure you take a printout of the link with you as you know the government employess in any country is pretty much like Shree Paanch ko Sarkar. Just in case, they make a scene, make sure you can produce the printout from UK Government's website on the visa requirement. The price seems to be cheap. Good for you bro.