Outside the hardcore crowd, online is mainly for those people who have left high school and/or college and moved away from most of their old friends, it gives us a way to play them since we can't just invite them over. That said, some games -- like Mario Party, for example -- clearly get the most enjoyment from the in-room antics during the game, and even with voice-chat the experience would be a bit more sterilized online.
I don't really care about playing random strangers online. And obviously without voice-chat providing some level of interactivity there's no point in online for me at all (which is where PS3 is lacking I hear due to no standard headset). Nintendo will also suffer from this; and I think they know that their games in particular have almost always been best with a group of people in the same room, it's the third-party games that'd benefit the most from online so Nintendo isn't real focused on it.