Even though that's the only reason he directly hints at, I also strongly suspect that:
1) Codemasters has a good deal of financial investment in the PS3/360 platforms in terms of graphica/physics assets and any long term software projects that take years to develop
Of course like most of the other 3rd parties they have invested most of their money in development for HD games, but that shouldn't stop them from bringing (some of) their franchises also over to the Wii. Not all of their games are highly demanding, like Micro Machines for example. That game is also a great local multiplayer game, so it should be a perfect fit for the Wii, don't you think?
Developing for the Wii doesn't mean that you have to target solely the new demographics, we have enough evidence that traditional games sell well on the Wii if they are good games. They don't have to shift most of their resources immediately over to the Wii, but they should try to get there over the course of the next couple of years. With the high userbase of the Wii, there is just too much money on table to ignore, no matter which type of game you produce (as long as it's a good game).