Hundreds of publishers including The Washington Post and The Wall Street Journal have signed on with Google’s Accelerated Mobile Pages platform to serve up hyper-speedy mobile versions of their stories, but the verdict on the effort’s revenue-worthiness is mixed. The problem is that Google is directing more traffic to AMP pages, where some publishers aren’t getting ad revenue at the same rate as their mobile sites, and AMP’s ad units are much more limited than other mobile ads, Mike Shields explains. WSJ subscribers can read more.