Under the definition you use, Buddhism is NOT a religion, it does NOT depend on any Supernatural justification. On the other hand most people call it a Religion.
More on Buddhism:
http://en.wikipedia.org/wiki/BuddhismAs to Economics being a Religion, a stronger argument for that can be made then Buddhism. Economist great founder was Adam Smith, viewed as the founder of Western Economics AND Marx called Adam Smith the most important economist prior to the raise of Communist Doctrine in the 1800s. The best example of this is the "Invisible hand of the Market Place" which has been used by Economists to justify what they say Economics is (The term is attributed to Adam Smith, but he did NOT use that phase in his Book on Economics).
More on the "Invisible hand of the Market Place":
http://en.wikipedia.org/wiki/Invisible_handNow, most people do not call the "Invisible hand" supernatural, but I am just pointing out that it can be viewed that way, much more then some of the Doctrine of Buddhism. Just pointing out, if your definition of Religion is a World View agreed by a group of people, Christianity, Buddhism, Marxism, and Western Economics all meet that test. If you add Supernatural belief to that definition, all but Christianity falls out of that test. Thus if Buddhism is a religion so is Marxism, and Western Economics, if Marxism, and Western Economics are NOT a religion neither is Buddhism.
Thus the better definition of Religion, is a World View adopted by a group of people. This is is line with various decisions of the US Supreme Court on the Issue of Religion than any requirement that the definition of Religion includes some Supernatural content.
One Last Comment, the Statistician W. Edwards Deming, once pointed out that Economics is NOT based on double blind side experiments, i.e. one thing change in the test group, and you have a control group without the change. Such double blind side experiments is the Holy Grail of any Scientific test, and a type of test NEVER done in Economics. Thus Deming refused to call Economics Science, for it failed that test, i.e. Economics is NOT based on double blind side tests, but observations that may or may not be valid for the subjects have other causes and input into their difference in actions in most Economics comparison.
More on Deming (Through NOT his comment on Economics):
http://en.wikipedia.org/wiki/W._Edwards_Deming