Weeellll....I'm sure you're aware that writers often use a certain flair to make the writing more interesting. So Sherlock Holmes might just be such a device, not to be taken quite this seriously. But as to the logical reasoning I'm quite serious...
So just to engage you here, because you raise some good points, but seem to misunderstand a few things, and it's fun:
"has the nasty habit of leaving you with an alternative that's equally improbable"
Well, yeah. The main thrust of the post wasn't Sherlock Holmes, the point is can't just say "it's improbable"...you have to compare apples to apples. The whole U-haul deal was improbable, but when you looked pretty close at the fact pattern, was it really all that more improbable than that Greyson AND Gorman, both park employees, were totally off their hat? That's why I gave full credit to the posters here - they addressed that problem fair and square and came up with answers that I thought were better than just dismissing them outright.
"Unfortunately the U-Haul theory in particular has the flavour of "If Officer Grayson is correct, then you inevitably come to a theory like the UHaul!" and this isn't really right."
No, it isn't, because Grayson's kind of irrelevant to the U-Haul. It would be closer to accurate to say if MIMI GORMAN is correct, then you inevitably come to a theory like the UHaul. Because Ms. Gorman insisted the car was the wrong way 'round. Grayson just said it wasn't there.
"If the ranger is correct, must there be foul play? Or is it merely likely that there is foul play?"
Well, again, let me correct the premise. When I was talking about eliminating foul play I specifically talked about THE INHOLDING. So to me, if you can eliminate a means by which Bill can encounter someone on his hike who does him harm and can get rid of his remains, you can pretty much eliminate foul play. Yes, it could have happened at the parking area, but one would expect there to be some evidence of that there, and there wasn't.
If the ranger AND GORMAN are both correct, yes, it increases the likelihood that there's foul play, but no, it doesn't directly infer that there WAS foul play (There's also self disappearance to contend with). I think I stated that, in pretty much those words.
"Could Bill have moved his car by himself while a search was underway for him"
Yup. Talked about that at some length too. I don't know if that could have happened "without realizing" but sure, maybe.
<<Sure, you can make a set of assumptions that seems reasonable to come to a possible conclusion, but who's to say one set of assumptions is better than any other?>>
Got into that at some length, too, on the first half of the blog. You compare and weigh objectively as best one can. Occam's Razor says, roughly, the hypothesis that requires the fewest assumptions is to be tested first.
I mean no disrespect, Osmanthus, but given the questions you raised I have to wonder if you actually read most of the blog. While I admit my reasoning and writing can be pretty dense at times, I did deal with most of them pretty clearly in the body of it, and for instance you keep talking about "the ranger" when there's a whole 'nuther park employee witness, Mimi Gorman, that directly inspired the U-Haul theory. If you are unfamiliar with her role in the case, and it would appear you are, yes, it would certainly seem like the U-Haul comes out of nowhere.
But to grapple with your central premise: it's simply not true that all assumptions are created equal and there's no way to assess them - nor that because we can't technically rule out any improbable scenario we can't rule out anything at all. Some things, such as UFO abductions, are technically possible but I think we can rule them out for the purposes of narrowing things down. Likewise to me if there's no way to deal with Bill's body logistically I don't see foul play as being very likely, even though there's a million scenarios you can come up with that are technically possible, but require too many leaps of faith to be true.
Some might say the U-Haul idea is up there with the UFO abduction, and all I can say to that is, I laid out my reasoning in favor of it, and when people came up with counterexplanations that explained those facts better, I agreed that they were more likely. I think that's pretty honest intellectually. YMMV, of course.
I'd be interested to hear your theory.