OK, let me reopen some discussion about this.
I have many different kinds of documents posted on my website for download. The only ones that end up with LOTS of 206-accesses are pdfs.
Yes, some ppts take a few accesses to get the whole thing, as do some mp3s, but this business with a hundred or more consecutive accesses, in 32K or 64K chunks, with 206 status code, is all about pdfs. All are of the same order of size -- about 2-10 MB.
As to mobile devices downloading small pieces, I've tried it with an iPhone and, at least with the iPhone connected to a local router, it gets them each in one fell swoop. That's not it.
So I still have the question. In my Apache logs, why do I often have GETs that require a vast number of accesses to get the whole thing? What makes that happen? These incomplete accesses make up about 20% of the lines in my Apache logs.