By not disabling the cache Safari will just reload the web page from disk, instead of downloading it all over wifi. In normal use you don't sit around reloading the same page all day, you surf to different web sites, so caching extends battery life to unrealistic levels.
Really? In normal use, people visit a very small subset of sites very frequently. I'd wager the majority just waste the day on facebook alone.
You, in all likelihood, visited this site twice already, once for the home page, and once to get to this article. Not to mention whatever happens after you submitted your post. Turning off cache would be far *less* realistic
Besides, it's not like Apple invented web caching just to inflate their battery performance. It exists in all browsers for a very good reason. And, the cause of the battery drain wasn't turning off the cache, it was the bug introduced by turning it off...