Even though you see the threads that complain about no movie playback on the Wii I think it's actually helping Nintendo by not having it. (I'm talking about disks based movies, not playing them in other ways like SD cards)
1. When asked, almost 70% of people are waiting until the outcome of the Blu-Ray/HDDVD war to pick a next gen player. A more telling number is that almost 40% think that ANY player purchased before the war is over is a waste. Mind you these numbers are from TV morning shows and was aimed at everyone which is mostly made up of REGULAR people, not video enthusiasts. Still, when 7 out of ten people are waiting and more then one third find anything now a waste it's pretty telling.
The Wii appeals to everyone so it makes sense that people are looking at the Wii as a game system and not looking at it as maybe the "Wrong horse in the race". This means that fewer people are being held back from getting a Wii. Especially the average people. They don't see a downside in the Wii when it comes to their multimedia systems planning for the future.
2. DVD's players are last gen. While DVD players were very expensive more then a half decade ago these days you can get a player for 30 dollars or less with more features then any console. This also plays into the "everyone" role.
Most users have a DVD player and don't see a point in getting another. Again, when people are looking at the Wii they're looking at a game system. They're not seeing it as a something that they already have 1 of. Sure some people don't have a DVD player and would like the ability to play them in the Wii but we're closing in on 2008, they're in the great minority these days and Nintendo is aiming for mass appeal this generation.
The Wii doesn't have anything to make the average consumer think "maybe I should wait". There are no battles in format holding them back and there's not a feeling of remorse from buying something they already have and don't need another.
I think the lack of movie support is a strength of the Wii with consumers, not a weakness.