I don't think it has to do with giving healers an "edge" and more so to do with trying not to encourage healer DPS being required.

With things the way they are now, very few statics are going to turn away healers for not having capped accuracy since they know the cost is quite high.

However, give healers free accuracy, and now statics will automatically expect you to do like 900 DPS or something.

This also causes DPS to become complacent, as if healers can bring 1000 DPS, that's 1000 less that they have to do. So a good healer can end up "carrying" some bad DPS.