Steam doesn't actually own Steam.com The current owners won't sell it.

Which is hilariously funny since there's nothing there but a drop page.

Folks that do that kind of irritate me. Sure, you can do what you like with the domain, but it's like they are being uncooperative for the sake of being uncooperative.

Yes, this is true. It looks like steam.com wasn't the particular case I was thinking of; one such instance with what must have been another company, the landing page basically made it clear the owner was squatting the domain to piss of the company that wanted it.

I wonder what they pay to serve it though, I wonder if there are enough hits to it for it to be non-trivial (where non-trivial for a drop site is more than spare change a month)

I'm curious as well. It's been like that for years from memory. What possible value could this site have for the owners? Apart from maybe trolling purposes? And just who are "Steam Tunnel Operations" anyway?

They do have an MX record present, so it's possible that they still use email for some legitimate purpose. Bear in mind they've had the domain since 1994 apparently (according to a WHOIS lookup), that length of time makes it unlikely that it's purpose is illegitimate.

   Name Server: NS1.VALVESOFTWARE.COM
   Name Server: NS2.VALVESOFTWARE.COM
   Name Server: NS3.VALVESOFTWARE.COM

Seems legit.

If you check the certificate for https://steamcommunity.com/, it should show Valve Corporation. Regardless, you can log in at the Steam store (https://store.steampowered.com/); the session should automatically transfer to Steam Community.

Valve does not have steam.com, the store site is steampowered.com and the community site is steamcommunity.com...

Steam's community domain has been what you'd mentioned since quite some time. No need to be hesitant.