I disagree. You can achieve a much more solid tie down with a block or some such between the tire and fender. I've had my bike fall over quite a few times because the forks weren't blocked. Never when using a fork support.
I'm going to suggest something wasn't being done right for that to happen.....
Bikes only fall over, or come undone when there isn't enough preload created by compressing the forks about 1/3 or more(about 4"), and/or the straps weren't attached properly. You have to get into the progression curve of the fork. The hooks on the straps have to be set in the attachment points properly (surprising how many guys don't do this properly) The ends of the hooks always should be facing up and out, never down and in.(millwrights know this). Better yet, use good carabiners.
The straps should be as close to 45 degrees as possible from bike to tie point on truck or trailer. Multiple bikes should be tied to each other as well as to the transport vehicle. (I can't believe how many guys tie the straps vertically, or close to vertically & the bike sways around like a drunk)
On trailers, bikes generally should be tied by an extra 2 points such as the footpegs, due to the extra bouncing a trailer goes thru.
I've seen unblocked bikes fall only when guys just compress the forks a tiny bit; say an inch or so, or didn't set their straps properly. I've also seen blocked bikes come undone as well for the same reasons.
You can't actually get a more solid tie down using a block vs without- you'd be breaking the law of physics.
Tiedowns always have to be in tension. An unblocked bike tied properly will keep more necessary tension on the straps vs a blocked bike.
Personally, I've tied hundreds, if not thousands of bikes down without blocks on trucks, trailers, carriers etc. never had one come loose.