The problem with this notion - as mentioned by a few people in the article's comments - is that it is difficult to find developers with a high level of expertise for both sides of the fence. Is it worth the extra expenditure of time in the hiring process to look for two people who are good in both realms? Or is it better to spend less time looking for one front-end expert (with passable server skills) and one server-side expert (with passable client skills)? My experience interviewing/hiring suggests the latter.

I will concede the obvious: if you find someone who is great on both sides, HIRE THEM. If you are lucky enough to hire that person, don't pigeon hole them.