I've been studying those links on that page for awhile. You did mention signs, so I guess you want me to look at the first caps.
I opened both up on high quality IPS monitors. I'm viewing these pictures on dual 24" Apple LED Calibrated screens.
Take a look at the very back sign that says "Salvation is Free". It's certainly about 5% clearer on the Blu-ray compared to the HD stream. However, I can still read the lettering on the HD-stream cap, which just states that the detail gain isn't significant (the DVD probably wouldn't allow you to make out anything back there
) and that it still may be due to artificial sharpening. Let's continue.
Another example of how I may be wrong, is look at the "We Moved" sign to the left of the image. I can clearly make it out on the BD, while on the HD stream I have to somewhat guess. This looks to be about 10% clearer, but it could likely be due to the artificial sharpening that helps make it stand out more. It really isn't the fine texture that's making it clearer (there is none in either cap), but more so with the artificial frequency tuning of the colors to make them "pop" out more.
So, I will admit, that the BD image shows 5-10% (10% being maximum) more detail in the first image. However, you also have to take into account, that the HD stream is a lousy MPEG-2 format running at a lousy bit-rate. Also, you'll have to take into account that in the other scenes (not in the first screencap), you'll actually see detail loss
in the BD for scenes that show an abundance of blacks (such as the band screencap), or scenes that have DNR smudging (such as Marty in the car seat screencap). So it's a give and take scenario that we have here when considering "detail gain".
So, it can be quite arguable whether the BD caps show more detail overall. Sometimes they do, and sometimes they don't. However, what isn't arguable, is that the HD streams are more natural and resemble what film should look like, and have little if any processing. Additionally, if you were to run the HD stream in a VC-1 or AVC codec, increase the bitrate without any DNR or EE, you would probably have something that would stomp the current BDs into oblivion. So in conclusion, the HDstream is still better overall due to the detail gain in many other areas while detail loss in some areas (which is mainly a codec/bitrate issue), less processing (no halos, smudging), and resembling a more natural image with film grain.
What would be really fun, is if someone had the HDstream for BBTF Part 3. I bet it looks gorgeous compared to the BTTF 3 BD, with a hands down victory without any debate needed.