Lbussy - I'm curious what your final pitching temperature is if you add at 104 and wait 20 minutes without doing anything. I'd be concerned about the difference in temp between the yeast and the wort that you're pitching to.
As you point out it is desirable to keep the temp swing < 18 degrees (or lower in some texts) so the yeast gradually cools. I introduce an equal quantity of must or wort over the following 5 minutes to help get the yeast eating and to further lower the temp. This is described in those texts I posted as well.
I agree that there's a lot of misinformation out there on this subject. I tried google again and found where I got the info stuck in my brain on the fact that DI water is bad.
I agree there, and the reference I posted says the same thing. When making beer I generally sanitize tap water in the microwave which I would guess gets rid of chloramines as well. When making wine I rarely go to that trouble, using my hot water out of the tap at 110 to mix in the GoFerm which generally leaves me at 104-ish.
The reason I bring that up is because fermentis actually recommends rehydrating US-05 in the 80s. Not trying to get into an argument, but 104F may be the target for lellemand yeasts, it may not be the end all be all.
I've read that, and to be brutally honest I wonder if they are correct, or if they are carrying over experience with live, vital yeasts into the dry area? How could dry yeast (of the same strain in a lot of cases) from one manufacturer rehydrate optimally at one temp, then from another rehydrate at a different temp? I've seen the micrographs (and I can't find them now of course) supporting the warmer temps but never seen the "science" behind the cooler temps. So, again being honest, I wonder if their science is correct because the rest of the world (who has been using dry yeast for quite a bit longer) thinks differently. Does Fermentis actually perform the processing, or do they contract it from other places? If it's the latter then there's little reason to suspect their yeast would miraculously behave differently. I do have a suspicion that it's a marketing decision - making your yeast easier to use (close enough is good enough?) makes it a contender in the market. Maybe we have a biologist here who can test for us someday.
Last, I think there's been taste tests that suggest no one can really tell the difference between direct pitching of dry yeast and rehydrating, so I'm not trying to act as if this will be the difference between good and bad beer.
If the beer is clean then the beer will be clean at the end. However, I have seen a drastic difference in fermentation characteristics between the two methods. Related to that but not within the same samples I have easily tasted the difference in a yeast-forward ale style when pitched properly, and under-pitched (in my mind this would emulate faulty rehydration). So while I am joining two separate experiments, there's a reasonable hypothesis there that dry yeast which is not rehydrated (which I have proven to myself ferments more sluggishly than properly hydrated yeast) will have a difference in the finished product. I agree that is not a scientific test, but it seems reasonable based on the other bodies of evidence available.
And lastly ... there is just a HUGE difference in "properly" rehydrated yeast's performance vs the "pitch and go". This post started because of concerns the OP had which are arguably tied to his treatment of the yeast. Since we all feel MUCH better when we see bubbling airliocks first thing in the morning after brewing, why not go with a method which produces that? Granted that's a "feel good" explanation but if we were not driven by what feels good we would not be making ethanol.