[objclxt]

You'd be surprised: the assets take up about 50% of the total. It's simple enough to examine the contents of an IPA file:

iBooks used to be under 20MB. Over time it's expanded to its current size of 50.8MB when it's uncompressed (the extra space it's taking up on your device is probably the books themselves).

The vast majority of that is images. Apple have at least been somewhat smart about it, choosing in certain cases to use lossy JPGs rather than PNGs where the user won't notice (the startup image, for example).

The app also ships with some custom fonts, which take up a few of those MB. The languages, which you suspect take up a lot of the space, actually don't represent that much: each language is about 45KB.

The executable itself is 25MB: so basically, 50% of the app size consists of assets. The percentage is probably higher on most other apps, because the iBooks executable is rather large (unusually so).

[pmjordan]

That indicates that shipping separate executables for armv6 and armv7 alone would save over 10MB. Holy shit. (yes, latest iBooks still works on the iPhone 3G)