I'm not sure it's something Facebook is necessarily pushing. I think it's just businesses squeezing e-commerce pages into Facebook page tabs.
I think a lot of folks still don't notice the custom page tabs. They "like" something and they see the items that get dumped into their stream as a result or they occasionally go to the "wall" for that thing, and just don't see the links in the sidebar to the custom pages.
Even if the company sets it as the default tab for their page, once the user has "liked" the page, the default changes to the wall.
I think it's because Facebook isn't officially enabling and supporting e-commerce that it's not working out well.
I think a lot of folks still don't notice the custom page tabs. They "like" something and they see the items that get dumped into their stream as a result or they occasionally go to the "wall" for that thing, and just don't see the links in the sidebar to the custom pages.
Even if the company sets it as the default tab for their page, once the user has "liked" the page, the default changes to the wall.
I think it's because Facebook isn't officially enabling and supporting e-commerce that it's not working out well.