Socializing starts with You. Only you can prevent anti-socialism.
Even little things like logging on your JC to cut a gem for some stranger in Trade, taking a lowbie on your two-seater mount to get his 1K FP, giving some extra mats for free to someone desperate, watching someone's pleas going up to 200g for one elemental earth and charging him 1g.
There are a lot of little things you can do to spread goodwill and kindness around your realm if you're not a greedy virtual-money grubbing heartless bastidge.
Play nicely together!!
And those little things you mention are part of why cross realm isn't a solution because you can't do most of those things cross realm. Those are the types of things that tend to start the lasting relatiionships. There's more to socializing that just saying "Hi" when someone on your friends list pops online.
Lots of people try to socialize in this game. I'll be on my bank alt posting auctions or sorting the odds and ends I've mailed from other toons. Someone will pipe up in trade "LFG random heroic" and you get a flood of "use DF noob". So many players are actually working counter to the social aspect instead of working with it that those who want to find it harder to make connections, assuming they don't end up discouraged completely.
For the purposes of top end game progression, whether PvP or PvE, socialization and communication are still mandatory. It's highly unlikely you're going to be able to get a random group of strangers together and get a realm first unless you're on a realm that is so low pop with progression so far behind other realms that the realm first is still out there waiting to be taken 4 months later.
But for other game content?
You can pug a group via trade, openraid, etc. and never talk to those players again.
You can queue for RDF and never see those players again.
You can queue for BGs and never see those players again.
You don't need a group to quest anymore because all the group quest content has been removed. I think there are only a couple of rares in Pandaria that aren't easily solo'd by any competent player.
You don't need to talk to other players to learn how to play your class better because that information is all googled.
You can set up multiple alts to cover all the professions so you don't have to ask another player to cut a gem, do an enchant, etc. for you.
There's really very little in the game you can't do without ever having to say a word to another player.
If you were to remove to remove all the other players except one from a realm and replace them with NPCs, that player would probably notice - and then not care after that first minute as long as when their BG or dungoen queue popped, there were enough in the group to finish the activity. Just random fill the AH with items like the BMAH will have items randomly added by the system.
This easily could be a single player game and most players would be just as happy because they no longer have any incentive to step out and socialize on a regular basis with others outside of raid and PvP progression.