Well, part of seeing the content is actually experiencing it, not just reading the lines the boss says and stuff. If that was all we cared about then we'd just download kill videos and watch those instead of putting in the effort to raid. When people say 'experiencing the content', at least the people I know, they're talking about getting 24 good players together, building a proper raid setup, and learning and downing a difficult boss. It really is an amazing feeling, and it won't be there in 10 mans. Kara was fun, but our first Prince/Nightbane/whatever isn't even comparable to our first Vashj/Kael/Illidan/Archi.
Interestingly enough, the guild quit raiding part way through Sunwell. Once 3.0 hit those of us remaining could've easily downed Kil'jaeden, but that was meaningless to most of us. A few people left and joined the top guild on the server and went on to kill KJ (they were 5/6 Sunwell pre 3.0). The people that left were all loot whores. Those of us that were really in it for the experience knew that the Sunwell experience was gone once 3.0 hit so we didn't bother.
Basically, 10 mans are easy mode and 25 mans are hard mode. The true experience and accomplishment from any game comes from beating it on hard mode.