Ironically, the people who would benefit most from building in the browser (i.e., the developers) prefer to create something shinier by going native. Maybe they won’t choose that path if there are four or more major platforms they have to support but until that happens, it’s telling that when the browser route is possible, developers pass on it.
As I've tweeted on a number of occasions, my perspective is that there won’t be one winner when it comes to the debate of native apps versus the mobile web. This article doesn’t imply that and in fact, is probably hotter on apps than most perspectives.
My comment above clarifies my thinking, which is that the browser won’t be a strong option unless there are simply too many native platforms to support. That would mean that Windows Phone 7 would need to become a strong apps player. It might.