Some of it is from falling behind, but a big part of the burden on web devs is that Safari updates just frequently break existing JS and webpages. I don't know

Some of it is from falling behind, but a big part of the burden on web devs is that Safari updates just frequently break existing JS and webpages. I don't know if it's because Apple has insufficient testing before releases or because they expect web devs to roll over and do what they want, but either way, it sucks. Back when Safari had windows builds, I at least made an effort to test locally and fix the bugs they kept introducing. But many of the bugs only reproduced on OS X, and now there's no Windows port, so there's no way I'm going to drop a bunch of money to buy a Mac just so I can do their work for them. Safari bugs have broken my JS more often than every other browser combined. IE included.