And *you* obviously have never run a tiny Internet-only business. I sell a couple of apps. Kind of the "in" thing to do these days, and it brings in just enough to pay for an occasional new device to write new apps for. I do my bookkeeping by hand with spreadsheets and a small database, because that's all it really needs.
I pay my state's business taxes, and sales tax on in-state purchases. By check, once a year. Manually. Last year, I remitted $.41 (that's 41 *cents*) spread across 5 different tax zones to cover the in-state sales taxes. It probably cost the State and those taxing areas hundreds if not *thousands* of times more than that just to process the payment. But, the law's the law.
Now say I have to track and pay sales taxes in *all* of the States. Not every state has an online lookup for all local taxes. A subscription to one of the commercial services would wipe out most of my profit for the year. Then there's the cost of mailing checks for a few cents to at least 50 taxing authorities (assuming that all of them even *take* checks).
If Apple, Google, Amazon, and all the other app stores don't pick up the burden of collecting the exact sales tax on each paid download, then most of the U.S. app developers are probably going to be forced out of business by the overhead.