(1) why would one need a "service" (much less a paid one) to find and download anything on Usenet, and
Say I'm looking for a very rare 78 record, Leo Blech conducting the Coriolan overture - - on Usenet. I will need some kind of search service to find it, and I may well find that paying is better than not paying, given how incredibly cumbersome the process of finding a binary file on usenet is.
(2) what would a *legal* copy of HTOED be doing on Usenet in the first place? It's a double oxymoron, stress on the last two syllables.
If it's a copy of the OUP-printed version (and what else is it likely to be?) then it is not legal. Also, BEWARE !!!! you don't really, except for boasting rights, want the print version. It is incredibly cumbersome to use by comparison with the computerized versions. Because once you find the sense you're looking for in Vol. 2, all you have is a long series of numbers. You now have to spend quite a bit of time getting to those numbers in Vol. 1. The best way to use the HTOED by far is paid via OUP or free via U of Glasgow.
That said, I suppose it is possible that someone might be able legally to grab the U of Glasgow data and present in a different manner. But who is actually going to do this? It would still take years to do at all well.