As a guy who has worked on the RTC on a modern SOC, I actually looked into this. There are lots of ARM-based computers without RTC's (and their batteries) and they get time as you suggested or similar methods.
The problem, as I understood it, when I asked repeatedly "why do we still use this ancient thing?" was, as I was told when we looked into it, was the same problem you have with all things x86 - which is that there are some legacy uses that still require it, some vendors still adamantly want it, and so when you say "hey, we are getting rid of it", they say "well, we aren't buying that chip then" or worse "we want your chip and we want RTC, we buy lots of your stuff, make it happen". A couple of our customers needed accurate time for systems that didn't get plugged in to the network or needed accurate time prior to accessing the network as part of the network access handshake, and so getting rid of it killed their business model.
Honestly, the RTC is a super irritating chunk of circuitry to put onto an IC - the voltage is super high for a 14nm CPU and getting it working is a very small part "fun engineering challenge" and a very large part "every CAD tool gives me totally bogus errors on this thing and I'm sick and tired of combing through dozens of logs files looking at thousands of errors and triple-checking that they are all bogus" tedious activity. I'd love to see it gone too and I mention that to my management every chance I can.
Patrick Mahoney
Intel Corp.
(not an Intel spokesperson, just a random engineer who works there).