At a TAXI Road Rally a speaker from ASCAP did a study on #1 songs in country and pop for structure and found that by far most of them had bridges. Does that make it a necessity? No. However when I do critique songs here, I find that most are without bridges. What many writers overlook is the emotional payoff in a song. Songs where the lyrics actually mean something should usually have a bridge to accomplish the emotional impact that will motivate the listener to like and buy the song. IT'S NO SALE IF YOU DON'T! So country and pop songs are likely to need bridges if they are to be commercially successful. The #1 Country Song on Ourstage in July was my personal choice for the top song. Yet I wrote the artist that a bridge would put it over the top. In instances like this, a bridge is the artist/songwriters conduit to commercial success as opposed to just having a popular likeable song.
Genre does determine the necessity of a bridge. A lot of us here who have commented write Novelty/Comedy songs. A bridge really isn't a necessity - and it's usually because there's no serious emotion involved.
In conclusion I would say if you're writing a serious tune and want to make an emotion impact - which is what will ultimately make a sale - use a bridge.

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