That all said i still think construct is awesome and am not meaning to put anyone down, just portability is good.
Of course it is. However, like it or not, DirectX is far more supported and used. It makes more sense to get DirectX working 110% before starting another API.
As for Vista, you're speaking as if there won't be a windows again down the road, and who is to say that won't be the most popular one yet?