I think what Thrayce Lanley said is true. Her analogy is not wrong, it's the right analogy. The most of the older users used the older viewer interface so long, that they used to it. (accustoms/customized)
One year ago, I came back from a longer SL-Break and found the new Viewer 2. Before my break, I used the old Viewer and the Emerald Viewer for a long long time. But I really like clean, understandable and workflow optimized user interfaces. The old ones was overfilled with functions and buttons, what for us old users don't really a problem, but for the new users Viewer 1 Interfaces was a big barrier.
I've tested Viewer 2 seven days long, and switched then back to Emerald. But I've found out of the benefits from the Viewer 2 and can't work without them anymore. Only the web-profiles bring me back to the ThirdPartyViewers, because this feature was so bad implemented and slowly that I can't like and work with it for a longer time. Thanks the Phoenix Project his Firestorm Viewer (which I really like since Beta 3, because V3-Interface-Mode), I avoid the official SL-Viewer.
Peggy Paperdoll, you can't say the TPVs like Phoenix/Emerald with the classic interface was more intuitive as the new one. It was the TPV-Community who pushed new users to use the TPV Viewers, so they don't have to work or know more about the Viewer 2. The most users I know cried like a baby and switched back in few hours, when they tested the Viewer 2. Then the tried to make the official Viewer bad for new users... No wonder that newbie's forced by the TPV-Community to use TPVs instead the official Viewer.
That don't mean I don't like TPVs, I use Firestorm and don't accept the new/slow web-profiles. I only don't understand the small-minded behave of the most V1 Interface Lovers.
I hope the Firestorm Project will going on and allow users to decide which interface type and behavior they used to. (between V1 and V2/3)