In the Westminster system, it has been the practice since Charles II that when it comes to money bills the Lower House ”shall not suffer the Lords to make any amendments on it” (in the words of the historian Henry Hallam).
All Bills for raising Revenue shall originate in the House of Representatives; but the Senate may propose or concur with Amendments as on other Bills.
All of the relevant English history up until 1787 was very well known to the American framers, who simply made a very different choice, a choice to deviate from the Westminster system for reasons ably explained by Joseph Story in his 1833 Commentaries (section 873, my emphasis):
It will be at once perceived, that the same reasons do not exist in the same extent, for the same exclusive right in our house of representatives in regard to money bills, as exist for such right in the British house of commons. It may be fit, that it should possess the exclusive right to originate money bills [a phrase by which Story, we can be sure, meant only tax bills, not also appropriations; see italics below--MJF]; since it may be presumed to possess more ample means of local information, and it more directly represents the opinions, feelings, and wishes of the people; and being directly dependent upon them for support, it will be more watchful and cautious in the imposition of taxes, than a body, which emanates exclusively from the states in their sovereign political capacity. But as the senators are in a just sense equally representatives of the people, and do not hold their offices by a permanent or hereditary title, but periodically return to the common mass of citizens; . . . and as all the states have a distinct local interest, both as to the amount and nature of taxes of every sort, which are to be levied, there seems a peculiar fitness in giving to the senate a power to alter and amend, as well as to concur with, or reject all money bills.
In short, the U.S. Senate is not the House of Lords, but a fully republican (albeit more federal than national) legislative body. Hence there is no need for the same amount of jealous exclusivity to the House of Representatives’ power of the purse as we find, for historic institutional reasons, in the British House of Commons.
In any event, Mark Steyn’s intervention did not help out the fundamental premise of Andy McCarthy’s original argument: that the origination clause applies to spending as well as taxation. And I find it notable that the House parliamentarian, of all people, reads the Constitution my way and not Andy’s, while so far not a single member of Congress has given voice to Andy’s version of constitutional principle.