That's not a big footprint for an app, especially compared with image assets, app code and CSS bundled alongside.
It also means being able to add more functionality at will without having to rebundle, or worse, work on basic functionality helpers. Just seems like wasted time for such a small improvement. These devices were built to have application code on them.
Zepto is 24k. Does that extra 70k really make that big of a difference? A single retina resolution png is going to be bigger than that. I think there are other reasons to consider a library that's tailored for mobile webkit but size doesn't seem like a dealbreaker.
