Probably because Apple doing it isn't as likely to ruin the web for everybody as Google doing it.
Only because Apple doesn't have enough marketshare. If everyone was using safari (probably including any browser on iOS which is just a reskin of safari) it would be just as bad. Maybe even worse, as you might get locked out of sites unless you are using apple hardware.
Really depends on the site. Our marketplace sees 50% Safari usage since 60% of the traffic is mobile and Safari has such high usage on mobile for our customers.