I disagree. If a mapping API vendor is required to (or tries to) stay within an agreed upon 'standard' API, then that could stifle features/innovation. They would have to all agree on a standard to, say, add polygonal overlays, or moving objects (e.g. tracking realtime position of other vehicles)
However, when this 'abstraction of API' is relegated to other projects (as he points out Mapstraction, OpenLayers, and MyMap do this, they don't just attempt it) then each of them can decide if they are a minimal set implementation (only allow what all allow), or a maximum set, or somewhere in between.
What is better if they just support mapping using data format standards. They should all consume open/non-partisan standards such as GPX, GeoRSS, GML, etc. That way someone doesn't necessarily need to know the entire API if they can just load and map their common data source.
Is there a way to vote for the anti-request. :)
cross-posted from comments on Geonames