I don't think it's that important to specify exact icon sizes. Authors
won't bother to accurately provide such detailed information, and
applications don't need it anyway.
iPhone shouldn't be a concern here. It isn't limited to 59x60
icons—Apple's own website uses 129x129
(http://www.apple.com/apple-touch-icon.png) and current EDGE network
iPhones won't use anything else than rel=apple-touch-icon.
My suggestion is to simply define rel=application-icon without extra
attributes.
There isn't much bandwidth to be saved. These icons are going to be
downloaded only once. 128x128 PNG icons take only 20-30kb.
Large PNG file + favicon for smallest sizes may be good enough in most
cases. In cases when icon design doesn't scale well, authors could provide
additional .ico/.icns files.
When website provides application icons (not favicon) in .icns or .ico
files, I think it can be reasonably assumed that these files contain all
sizes that are needed for desktop icons, and it doesn't matter which
exactly.
--
regards, Kornel Lesiński
