Personally, I believe this is the way to go.
People have now assumed that Nintendo isn't taking this Games Convention seriously...and are assuming no release information will be announced, and very little new information will come out.
Well, Nintendo still is having a pretty big presence there with a keynote speech and I think a press conference event before the show. That sounds like something big is going down.
The idea of keeping the Wii gameplay to Media means that Nintendo will be able to allow the media (which will shape opinion of their readers) the opportunity to get more time with the games. This is more important than letting regular showgoers an attempt to play the system.
It also allows Nintendo to keep the price of this convention down, because they don't a large showroom floor presence.
I saw Kudos for Nintendo...and lets keep this positive instead of negative.