For a bit more context, the technology that allows the client to communicate to the server which hostname it is attempting to connect to is called Server Name Indication.
No it isn't fixed for all devices. Windows XP is one example and even though it is no longer supported by Microsoft, at least 17% of devices on the internet are still using it.
You can get a PTR from an IP address, but that's not the same as "the hostname the client requested". If virtuous_activities.com and shameful_fetishes.com both resolve to the same IP address (assuming some application protocol like HTTP that can distinguish by hostname) I could certainly imagine a situation where a client would want to keep the particular hostname requested secret.
(Obviously the attacker in this case would probably also be able to sniff the requests from the resolver, but still; I'm not making this complaint up or anything, a lot of people have mentioned it before.)
Huh? I used to have ~100 hosting clients per IP address, none of whom were in any way related to each other (other than in having chosen me as a hosting provider).
Actually I think it's quite common, it applies to any site not busy enough to justify a dedicated server. By the long tail principle that will be the majority of sites on the internet.
Oh, I should be clear, I'm specifically talking about sites sharing a certificate. I know a lot of sites use shared hosting, but it's awkward to get a certificate for a pile of unconnected sites. Most of them will either not support HTTPS or require paying a couple dollars for an IP. (Or, these days, try to rely on SNI.)
