The skin will not have all the features of the app or of the full site.
Bit disappointing to be honest. I'm sure the iPhone App (which I really liked on my mobile even vs the recently introduced mobile skin) could be "refreshed" with minor efforts and the skin could at least be improved for feature parity.
What are you usage stats showing ? I can't imagine that mobile access is decreasing (unless, obliviously, you want to make the site mobile unfriendly) ?
Just my 2c...