Ug, this is like the bad old days of 1995 when people made sites that said "Best Viewed with Netscape." I thought that was gone forever, along with splash pages and "under construction" gifs.
If most mobile browsers' support for javascript is limited or nonexistent, then it makes sense to optimize for Safari, since iPhone users will be the only ones able to use it anyway.
Anyhow, I tried the app out, and I can't decide if it's really useful.
I think it is pretty smart. I think I will try something similar in my mobile applications.