They acknowledge that it will make beer if you just sprinkle it into the wort. The vials from WL and the smack packs from Wyeast also say you can pitch them without a starter. Again, it will make beer. Neither of those suggestions is optimal.
There just simply is no debate about what happens when you sprinkle dry yeast into wort. You kill a large percentage of them.
If your recipe calls for an ounce of Cascade hops at 20 minutes, do you toss in half an ounce of old, dried up, stale hops you found loose underneath your refrigerator the last time you cleaned under there and just say "eff it, this will be good enough"? Of course not. Why would you exercise what is essentially the same mentality when it comes to the yeast?
From Fermentis (
http://www.brewwithfermentis.com/tips-tricks/yeast-rehydration/):
From Danstar (
http://www.danstaryeast.com/about/frequently-asked-questions):
Here is yet another resource about proper handling of dry yeast, from Dr. Clayton Cone:
http://home.comcast.net/~mzapx1/FAQ/Rehydrate.pdf
I am still of the "Do what you like" mindset, because you have to drink your beer and not me. That said, you really shouldn't be advising people to do something that is a proven bad practice and telling them it doesn't make a difference. It does make a difference.