"My home page goes from 31,803 bytes to 71,488 because of the JavaScript I've added to track visitors to my page and what they do. "
Using bytes to make it sound extreme is just silly. 70KB is hardly relevant today.
That mentality got us into this mess in the first place.
>When we plotted the data geographically and compared it to our total numbers broken out by region, there was a disproportionate increase in traffic from places like Southeast Asia, South America, Africa, and even remote regions of Siberia... Large numbers of people who were previously unable to use YouTube before were suddenly able to.
Granted, that's a bigger leap than the one that made you cringe, but if it takes 2 minutes to load the new version in these areas (the number Zacharias gives), cutting 40 KB saves them 30 seconds.
The full article: http://blog.chriszacharias.com/page-weight-matters.
With all the round trips that TCP/IP makes, and the congestion control and TCP slow start (especially if your connection occasionally drops packets, which often happens on mobile / wireless connections), surprisingly little additional data can add a surprisingly long delay. Especially considering the multiple round-trips to third-party servers often required by JS libraries.