There might be more to Snow Leopard than meets the eye, as rumors have emerged outlining tremendous cuts in application size for 10.6. Mail.app will drop from 287MB to 91MB, iChat from 111MB to 52MB, and iCal from 89MB to 48MB. Cuts are practically universal, with already small apps like the 13MB Calculator, 15MB Image Capture and 22MB TextEdit each to be recoded to a svelte 2MB or less. As a whole, the Snow Leopard's Utilities folder will take up just 25% of the space that it does in 10.5.
AppleInsider chalks the size decreases up to wider use of vector graphics and a centralized localization scheme, so as to prevent redundant language installations. More likely, however, is that the exclusion of PowerPC support has allowed for some serious pruning, allowing Apple to shed years of IBM residue from each app.
Additional reports confirm, as previously reported, that ZFS will be include in Snow Leopard Server, and claim that new text processing features (like autocorrect and text insertion) will be implemented system-wide, and that a multitouch programming tools will be supplied to developers for inclusion into their 3rd party apps. It looks like Apple is committing to the strategy of optimizing and improving upon an existing product instead of pushing for conspicuous new features, which is bold, to say the least
UPDATE: Macrumors has an interesting post that could explain the reduced sizes. Apparently if you remove extra languages as well as .nib bundles (essentially interface layout instructions, used during the compiling process for the application), you can reach sizes close to those advertised in the original post. [AppleInsider]