Is it acceptable to say "more [adjective]" when there is already a dedicated form making "more" unnecessary (e.g. "angrier" vs. "more angry")?

For years, it irritated me that people kept using "more [adjective]" where there were already dedicated forms making "more" unnecessary. For example, people would say "more tight" than "tighter". I figured people were just being forgetful, but then I see notable publications like The New York Times using "more angry" instead of "angrier".

"They were more angry with Washington and intense in their desires for a smaller federal government and deficit."

http://www.nytimes.com/2010/04/15/us/politics/15poll.html

I've researched online, and I don't see any clear indication that both are acceptable.

Is "more angry" correct and acceptable in this case?

In your Washington Post example,

They were more angry with Washington and intense in their desires for a smaller federal government and deficit.

I think that the "more angry" phrasing may be intended as a smoother read for the parallel construction ('more angry ... and (more) intense'), although if that's what they really intended then the second 'more' should probably have been included. Even so, though, perhaps the editor there felt that mixing a single-word comparative form (angrier) with an absolute form (intense) was something to avoid.