The reason for the focus on smaller servers is a result of several things. Mainly the fact that antigriefing for the normal admin is annoying, theres way too many ways to run minecraft servers, and the difficulty of getting your friends/playerbase to set it up like your mod. Mojang is killing their own game this way. The only reason it hasn't hit them at all is because minecraft is still becoming/is very successful (lol). I still see it getting picked up by friends at 25$, and no sales ever. It also doesn't need mods to be an amazing kid friendly game with hours of playtime.
Little off-topic, but this is why I see Minecraft as being an amazing business regardless of mod offerings, and will always be successful/profitable:
Legos. Fun, right? All kids love Legos, even some/most adults. Some kids can play Legos for 30 minutes and become bored and just don't enjoy them as much as others. Some can play with it for days, even years and never get bored; they find new ways to use the blocks. The point is, Legos aren't a love it/hate it relationship (unless your a parent, damn land mines). You can build anything you want with what they supply. Lego company adds new blocks every year and stops making certain blocks, so users keep having new items to drool over or build their ideas with. After a certain point, the lego company could just produce what they have and still have an AMAZING business. Legos, however, have to be MADE from plastic.
Minecraft, is a LOT like legos, except it has some HUGE advantages. One, its a one-time cost. you buy it once, and you get to have infinite fun. It's hardware (legos) vs software (Minecraft). Software takes nothing to make resource-wise but time, and plenty of users have time to make new stuff unlike in hardware where you need to actually craft the items. Two, it's like Legos in terms of kid-friendly: you can give your kids legos and not worry about much unless they are younger than 5-6 which is the lego-edible range. With minecraft, you don't even HAVE that issue. Three, it has a low startup cost. you can play minecraft on pretty much any newer pc without issues. 25$ is cheaper than most games for the DS, etc. that kids buy.
The moral of the story is Minecraft will never fail. Mojang could do NOTHING with the game, and it would still be profitable 10 years from now. Mods aren't important at all unless Mjoang wants more money. Money really isn't an issue at the moment, considering they don't even need sales to have waves of purchases related to a youtube video, etc. It's really the perfect storm of video games.